U.S. patent application number 11/404232 was filed with the patent office on 2006-10-26 for display device.
This patent application is currently assigned to Samsung Electronics Co., LTD.. Invention is credited to Akira Hirai.
Application Number | 20060238679 11/404232 |
Document ID | / |
Family ID | 37186470 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060238679 |
Kind Code |
A1 |
Hirai; Akira |
October 26, 2006 |
Display device
Abstract
An optical system consisting of a reflective polarizer, a
.lamda./4 retarder, and a functional transparent plate with first
facets and second facets which is provided on a display panel
assembly improves utilization efficiency of exterior light, so that
display luminance of a reflective or a transmissive LCD operating
in a reflection mode is improved. In another embodiment, an optical
system consisting of a .lamda./4 retarder, a selective reflection
layer, and a functional transparent plate with first facets and
second facets may be used.
Inventors: |
Hirai; Akira; (Seongnam-si,
KR) |
Correspondence
Address: |
PATENT LAW GROUP LLP
2635 NORTH FIRST STREET
SUITE 223
SAN JOSE
CA
95134
US
|
Assignee: |
Samsung Electronics Co.,
LTD.
|
Family ID: |
37186470 |
Appl. No.: |
11/404232 |
Filed: |
April 14, 2006 |
Current U.S.
Class: |
349/117 |
Current CPC
Class: |
G02F 1/133638 20210101;
G02F 2413/03 20130101; G02F 1/133562 20210101; G02F 1/133543
20210101; G02F 1/133536 20130101; G02F 1/133555 20130101; G02F
1/13355 20210101; G02F 1/13363 20130101; G02F 1/133538 20210101;
G02F 1/133528 20130101 |
Class at
Publication: |
349/117 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2005 |
KR |
10-2005-0034414 |
Apr 26, 2005 |
KR |
10-2005-0034416 |
Claims
1. A display device comprising: a display panel assembly; a
reflective polarizer that is provided above the display panel
assembly to transmit external incident light which is linearly
polarized in a first direction and to reflect external incident
light which is linearly polarized in a second direction
perpendicular to the first direction; a first .lamda./4 retarder
that is provided on the reflective polarizer; and a functional
transparent plate that is provided on the first .lamda./4 retarder
and which has a top surface including portions without a
cholesteric liquid crystal material and portions with a cholesteric
liquid crystal material.
2. The display device of claim 1, further comprising a second
.lamda./4 retarder that is provided between the reflective
polarizer and the display panel assembly.
3. The display device of claim 2, further comprising a first
absorbing polarizer that is provided between the second .lamda./4
retarder and the reflective polarizer.
4. The display device of claim 1, further comprising a second
absorbing polarizer that is provided under the display panel
assembly.
5. The display device of claim 4, further comprising a third
.lamda./4 retarder that is provided between the second absorbing
polarizer and the display panel assembly.
6. The display device of claim 1, wherein the reflective polarizer
utilizes a dual brightness enhancement film (DBEF) that is produced
based on reflectance anisotropy caused by refractive index
anisotropy, or delicate linear patterns.
7. The display device of claim 1, further comprising a backlight
unit that is provided under the display panel assembly.
8. The display device of claim 1, wherein the display panel
assembly, the reflective polarizer, the first .lamda./4 retarder,
and the functional transparent plate are bonded by an adhesive
agent.
9. The display device of claim 1, wherein spaces are formed between
the functional transparent plate and the first .lamda./4 retarder
due to a surface structure of either of a bottom surface of the
functional transparent plate or a top surface of the first
.lamda./4 retarder, and the spaces are filled with a filling
material with a refractive index that is equal to an average of
refractive indices of the functional transparent plate and the
first .lamda./4 retarder.
10. The display device of claim 9, wherein the filling material for
the spaces comprises an organic silicon-based material such as
silicon resin.
11. The display device of claim 1, wherein the display panel
assembly includes an LC layer with LC molecules that are aligned in
a 90.degree.-twisted nematic (TN) mode, a vertical alignment (VA)
mode, an electrically controlled birefringence (ECB) mode, or an
in-plane switching (IPS) mode.
12. The display device of claim 1, wherein the top surface of the
functional transparent plate has a plurality of prisms consisting
of first facets, on which a cholesteric liquid crystal layer does
not exist, and second facets, on which a cholesteric liquid crystal
exists.
13. The display device of claim 1, wherein the portions without the
cholesteric liquid crystal material and the portions with the
cholesteric liquid crystal material of the top surface of the
functional transparent plate reflect light once, respectively, so
that the reflected light is returned toward the first .lamda./4
retarder again.
14. The display device of claim 1, wherein the functional
transparent plate has a top surface with an embossed carving or a
depressed carving pattern and a bottom surface with an embossed
carving or a depressed carving pattern, and apexes formed in the
patterns of the two surfaces are formed to deviate from one
another.
15. A display device comprising: a display panel assembly; a first
.lamda./4 retarder that is provided on the display panel assembly;
a reflective polarizer that is provided above the first .lamda./4
retarder to transmit incident light which is linearly polarized in
a first direction and to reflect incident light which is linearly
polarized in a second direction perpendicular to the first
direction; a second .lamda./4 retarder that is provided on the
reflective polarizer; a functional transparent plate that is
provided on the second .lamda./4 retarder and which has a top
surface with first facets and second facets, wherein the second
facets transmit only a component of incident light which is
polarized in a specific direction and reflect the remaining
components; a third .lamda./4 retarder that is provided under the
display panel assembly; and a lower polarizer that is provided
under the third .lamda./4 retarder.
16. The display device of claim 15, wherein the second facets that
are formed at the top surface of the functional transparent plate
have a cholesteric liquid crystal layer thereon.
17. The display device of claim 15, further comprising an upper
polarizer that is provided between the first .lamda./4 retarder and
the reflective polarizer.
18. The display device of claim 15, wherein the reflective
polarizer utilizes a dual brightness enhancement film (DBEF) that
is produced based on reflectance anisotropy caused by the
refractive index anisotropy, or delicate linear patterns.
19. The display device of claim 18, further comprising a backlight
unit that is provided under the lower polarizer.
20. The display device of claim 15, wherein the functional
transparent plate, the second .lamda./4 retarder, the reflective
polarizer, the first .lamda./4 retarder, the display panel
assembly, the third .lamda./4 retarder, and the lower polarizer are
bonded by an adhesive agent.
21. The display device of claim 15, wherein spaces are formed
between the functional transparent plate and the second .lamda./4
retarder due to a surface structure of either of a bottom surface
of the functional transparent plate or a top surface of the second
.lamda./4 retarder, and the spaces are filled with a filling
material with a refractive index that is equal to an average of
refractive indices of the functional transparent plate and the
second .lamda./4 retarder.
22. The display device of claim 21, wherein the filling material
for the spaces comprises an organic silicon-based material such as
silicon resin.
23. The display device of claim 15, wherein the second facets which
are formed at the top surface of the functional transparent plate
only transmit either of a right-handed circularly polarized
component or a left-handed circularly polarized component of
incident light and reflect the remaining components.
24. The display device of claim 15, wherein the top surface of the
functional transparent plate has a prismatic structure including
the first facets, on which a cholesteric liquid crystal layer does
not exist, and the second facets, on which a cholesteric liquid
crystal exists.
25. The display device of claim 15, wherein the first facets and
the second facets which are formed at the top surface of the
functional transparent plate reflect light which is incident from
the second .lamda./4 retarder once, respectively, so that the
reflected light is returned toward the second .lamda./4 retarder
again.
26. The display device of claim 15, wherein the functional
transparent plate has a top surface with an embossed carving or a
depressed carving pattern and a bottom surface with an embossed
carving or a depressed carving pattern, and apexes formed in the
patterns of the two surfaces are formed to deviate from one
another.
27. A display device comprising: a display panel assembly; a first
.lamda./4 retarder that is provided on the display panel assembly;
a reflective polarizer that is provided above the first .lamda./4
retarder to transmit incident light which is linearly polarized in
a first direction and to reflect incident light which is linearly
polarized in a second direction perpendicular to the first
direction; a second .lamda./4 retarder that is provided on the
reflective polarizer; and a functional transparent plate that is
provided on the second .lamda./4 retarder and which has a top
surface with first facets and second facets, wherein the second
facets transmit only a component of incident light which is
polarized in a specific direction and reflect the remaining
components.
28. The display device of claim 27, wherein the second facets which
are formed at the top surface of the functional transparent plate
have a cholesteric liquid crystal layer thereon.
29. The display device of claim 27, wherein the second facets which
are formed at the top surface of the functional transparent plate
only transmit either of a right-handed circularly polarized
component or a left-handed circularly polarized component of
incident light and reflect the remaining components.
30. The display device of claim 27, wherein the top surface of the
functional transparent plate has a prismatic structure including
the first facets, on which a cholesteric liquid crystal layer does
not exist, and the second facets, on which a cholesteric liquid
crystal exists.
31. The display device of claim 27, wherein the functional
transparent plate has a top surface with an embossed carving or a
depressed carving pattern and a bottom surface with an embossed
carving or a depressed carving pattern, and apexes formed in the
patterns of the two surfaces are formed to deviate from one
another.
32. The display device of claim 27, wherein the first facets and
the second facets which are formed at the top surface of the
functional transparent plate reflect light which is incident from
the second .lamda./4 retarder once, respectively, so that the
reflected light is returned toward the second .lamda./4 retarder
again.
33. The display device of claim 33, wherein spaces are formed
between the functional transparent plate and the second .lamda./4
retarder due to a surface structure of either of a bottom surface
of the functional transparent plate or a top surface of the second
.lamda./4 retarder, and the spaces are filled with a filling
material with a refractive index that is equal to an average of
refractive indices of the functional transparent plate and the
second .lamda./4 retarder.
34. The display device of claim 33, wherein the filling material
for the spaces comprises an organic silicon-based material such as
silicon resin.
35. A display device comprising: a display panel assembly; a
selective reflection layer that is provided above the display panel
assembly to transmit a component of exterior incident light which
is circularly polarized in a first direction and to reflect a
component of exterior incident light which is circularly polarized
in a second direction perpendicular to the first direction; and a
functional transparent plate that is provided on the selective
reflection layer and which has a top surface including portions
without a cholesteric liquid crystal material and portions with a
cholesteric liquid crystal material.
36. The display device of claim 35, further comprising a first
polarizer that is provided between the selective reflection layer
and the display panel assembly.
37. The display device of claim 36, further comprising a first
.lamda./4 retarder that is provided between the first polarizer and
the display panel assembly.
38. The display device of claim 36, further comprising a second
.lamda./4 retarder that is provided between the selective
reflection layer and the first polarizer.
39. The display device of claim 35, further comprising a second
polarizer that is provided under the display panel assembly.
40. The display device of claim 39, further comprising a third
.lamda./4 retarder that is provided between the second polarizer
and the display panel assembly.
41. The display device of claim 35, wherein the selective
reflection layer is formed of a cholesteric liquid crystal
material.
42. The display device of claim 35, further comprising a backlight
unit that is provided under the display panel assembly.
43. The display device of claim 35, wherein the display panel, the
selective reflection layer, and the functional transparent plate
are bonded using an adhesive agent.
44. The display device of claim 35, wherein spaces are formed
between the functional transparent plate and the selective
reflection layer due to a surface structure of either of a bottom
surface of the functional transparent plate or a top surface of the
selective reflection layer, and the spaces are filled with a
filling material with a refractive index that is equal to an
average of refractive indices of the functional transparent plate
and the selective reflection layer.
45. The display device of claim 44, wherein the filling material
for the spaces comprises an organic silicon-based material such as
silicon resin.
46. The display device of claim 35, wherein the display panel
assembly includes an LC layer with LC molecules that are aligned in
a 90.degree.-twisted nematic (TN) mode, a vertical alignment (VA)
mode, an electrically controlled birefringence (ECB) mode, or an
in-plane switching (IPS) mode.
47. The display device of claim 35, wherein the top surface of the
functional transparent plate has a plurality of prisms consisting
of first facets, on which a cholesteric liquid crystal layer does
not exist, and second facets, on which a cholesteric liquid crystal
exists.
48. The display device of claim 35, wherein the first facets and
the second facets formed at the top surface of the functional
transparent plate reflect light which is incident from the
selective reflection layer once, respectively, so that the
reflected light is returned toward the selective reflection layer
again.
49. The display device of claim 35, wherein the functional
transparent plate has a top surface with an embossed carving or a
depressed carving pattern and a bottom surface with an embossed
carving or a depressed carving pattern, and apexes formed in the
patterns of the two surfaces are formed to deviate from one
another.
50. A display device comprising: a display panel assembly; a first
.lamda./4 retarder that is provided on the display panel assembly;
a first polarizer that is provided on the first .lamda./4 retarder,
wherein the first polarizer transmits external incident light which
is linearly polarized in a first direction and reflects external
incident light which is linearly polarized in a second direction
perpendicular to the first direction; a second .lamda./4 retarder
that is provided on the first polarizer; a selective reflection
layer that is provided on the second .lamda./4 retarder to transmit
a component of incident light which is circularly polarized in a
third direction and to reflect a component of incident light which
is circularly polarized in a fourth direction perpendicular to the
third direction; a functional transparent plate that is provided on
the selective reflection layer and which has a top surface with
first facets and second facets, wherein the second facets transmit
only a component of incident light which is polarized in a specific
direction and reflect the remaining components; a third .lamda./4
retarder that is provided under the display panel assembly; and a
second polarizer that is provided under the third .lamda./4
retarder.
51. The display device of claim 50, wherein the second facets which
are formed at the top surface of the functional transparent plate
have a cholesteric liquid crystal layer thereon.
52. The display device of claim 50, wherein the selective
reflection layer is formed of a cholesteric liquid crystal
material.
53. The display device of claim 50, further comprising a backlight
unit that is provided under the second polarizer.
54. The display device of claim 50, wherein the functional
transparent plate, the selective reflection layer, the second
.lamda./4 retarder, the first polarizer, the first .lamda./4
retarder, the display panel assembly, the third .lamda./4 retarder,
and the second polarizer are bonded by an adhesive agent.
55. The display device of claim 50, wherein spaces are formed
between the functional transparent plate and the selective
reflection layer due to a surface structure of either of a bottom
surface of the functional transparent plate or a top surface of the
selective reflection layer, and the spaces are filled with a
filling material with a refractive index that is equal to an
average of refractive indices of the functional transparent plate
and the selective reflection layer.
56. The display device of claim 55, wherein the filling material
for the spaces comprises an organic silicon-based material such as
silicon resin.
57. The display device of claim 50, wherein the second facets which
are formed at the top surface of the functional transparent plate
only transmit either of a right-handed circularly polarized
component or a left-handed circularly polarized component of
incident light and reflect the remaining components.
58. The display device of claim 50, wherein the top surface of the
functional transparent plate has a prismatic structure including
the first facets, on which a cholesteric liquid crystal layer does
not exist, and the second facets, on which a cholesteric liquid
crystal exists.
59. The display device of claim 50, wherein the first facets and
the second facets which are formed at the top surface of the
functional transparent plate reflect light which is incident from
the selective reflection layer once, respectively, so that the
reflected light is returned toward the selective reflection layer
again.
60. The display device of claim 50, wherein the functional
transparent plate has a top surface with an embossed carving or a
depressed carving pattern and a bottom surface with an embossed
carving or a depressed carving pattern, and apexes formed in the
patterns of the two surfaces are formed to deviate from one
another.
61. A display device comprising: a display panel assembly; a first
.lamda./4 retarder that is provided on the display panel assembly;
a first polarizer that is provided on the first .lamda./4 retarder,
wherein the first polarizer transmits light which is linearly
polarized in a first direction and reflects light which is linearly
polarized in a second direction perpendicular to the first
direction; a second .lamda./4 retarder that is provided on the
first polarizer; a selective reflection layer that is provided on
the second .lamda./4 retarder to transmit light which is circularly
polarized in a third direction and to reflect light which is
circularly polarized in a fourth direction opposite to the third
direction; and a functional transparent plate that is provided on
the selective reflection layer and which has a top surface with
first facets and second facets, wherein the second facets transmit
only light which is polarized in a specific direction and reflect
the remaining light.
62. The display device of claim 61, wherein the second facets which
are formed at the top surface of the functional transparent plate
have a cholesteric liquid crystal layer thereon.
63. The display device of claim 61, wherein the second facets which
are formed at the top surface of the functional transparent plate
only transmit either of a right-handed circularly polarized
component or a left-handed circularly polarized component of
incident light and reflect the remaining components.
64. The display device of claim 61, wherein the top surface of the
functional transparent plate has a prismatic structure including
the first facets, on which a cholesteric liquid crystal layer does
not exist, and the second facets, on which a cholesteric liquid
crystal exists.
65. The display device of claim 61, wherein the first facets and
the second facets which are formed at the top surface of the
functional transparent plate reflect light which is incident from
the selective reflection layer once, respectively, so that the
reflected light is returned toward the selective reflection layer
again.
66. The display device of claim 61, wherein the functional
transparent plate has a top surface with an embossed carving or a
depressed carving pattern and a bottom surface with an embossed
carving or a depressed carving pattern, and apexes of the patterns
of the two surfaces are formed to deviate from one another.
67. The display device of claim 61, wherein spaces are formed
between the functional transparent plate and the selective
reflection layer due to a surface structure of either of a bottom
surface of the functional transparent plate or a top surface of the
selective reflection layer, and the spaces are filled with a
filling material with a refractive index that is equal to an
average of refractive indices of the functional transparent plate
and the selective reflection layer.
68. The display device of claim 67, wherein the filling material
for the spaces comprises an organic silicon-based material such as
silicon resin.
Description
BACKGROUND OF THE INVENTION
[0001] (a) Field of the Invention
[0002] The present invention relates to a transflective liquid
crystal display or a reflective liquid crystal display.
[0003] (b) Description of the Related Art
[0004] Generally, a liquid crystal display (LCD) includes a pair of
panels individually having electrodes on their inner surfaces, and
a dielectric anisotropy liquid crystal (LC) layer interposed
between the panels. In an LCD, a variation of a voltage difference
between the field generating electrodes, i.e., a variation in the
strength of an electric field generated by the electrodes, changes
the transmittance of light passing through the LCD, and thus
desired images are obtained by controlling the voltage difference
between the electrodes.
[0005] Depending on the kinds of light source used for image
display, LCDs are divided into three types: transmissive,
reflective, and transflective. In transmissive LCDs, pixels are
illuminated from behind using a backlight. In reflective LCDs, the
pixels are illuminated from the front using incident light
originating from the ambient environment. The transflective LCDs
combine transmissive and reflective characteristics. Under medium
light conditions such as in an indoor environment, or under
complete darkness conditions, these LCDs are operated in a
transmissive mode, while under very bright conditions such as in an
outdoor environment, they are operated in a reflective mode.
[0006] In the reflective LCDs and the transflective LCDs, two
absorbing polarizers, which are films produced by adding iodine
molecules or bichromatic dyes to stretched PVA, are individually
attached to the outer surfaces of the panels. In general, the
absorbing polarizers have unique optical characteristics. That is,
they allow only P-waves of incident light to pass and absorb
S-waves. Theoretically, an absorbing polarizer transmits 50% of
incident light and absorbs the remaining 50%. However, the
absorbing polarizer actually transmits only 43% to 45% due to a
light loss at its surface. In the case when the light passing
through the absorbing polarizer is returned to the same polarizer
again by reflection at a reflective electrode, the transmittance of
the light passing through the polarizer again is only 39% to 41%,
even if the reflectance at the reflective electrode is 100% and the
color filters cause no light loss. Accordingly, the actual
transmittance is less than 39% to 41% because the color filters
used for the color display cause a light loss and also because the
actual reflectance at the reflective electrode is not 100%.
SUMMARY OF THE INVENTION
[0007] An objective of the present invention is to improve
visibility and display luminance of an LCD operating in reflective
mode.
[0008] To achieve the objective, a reflective LCD or an
transmissive LCD of the present invention utilizes an optical
system consisting of a reflective polarizer, a .lamda./4 retarder,
and a functional transparent plate with first facets and second
facets, which are disposed on a display panel assembly in that
order. Otherwise, another optical system may be utilized, which
consists of a .lamda./4 retarder, a selective reflection layer, and
a functional transparent plate with first facets and second facets,
which are disposed on a display panel assembly in that order.
[0009] In detail, according to an aspect of the present invention,
there is provided a display device including: a display panel
assembly; a reflective polarizer that is provided above the display
panel assembly to transmit external incident light which is
linearly polarized in a first direction and to reflect external
incident light which is linearly polarized in a second direction
perpendicular to the first direction; a first .lamda./4 retarder
that is provided on the reflective polarizer; and a functional
transparent plate that is provided on the first .lamda./4 retarder
and which has a top surface including portions without a
cholesteric liquid crystal material and portions with a cholesteric
liquid crystal material.
[0010] The display device may further include a second .lamda./4
retarder that is provided between the reflective polarizer and the
display panel assembly, a first absorbing polarizer that is
provided between the second .lamda./4 retarder and the reflective
polarizer, a second absorbing polarizer that is provided under the
display panel assembly, and a third .lamda./4 retarder that is
provided between the second absorbing polarizer and the display
panel assembly.
[0011] The reflective polarizer may be utilize a dual brightness
enhancement film (DBEF) that is produced based on reflectance
anisotropy caused by refractive index anisotropy, or delicate
linear patterns.
[0012] The display device may further include a backlight unit that
is provided under the display panel assembly.
[0013] In this device, the display panel assembly, the reflective
polarizer, the first .lamda./4 retarder, and the functional
transparent plate may be bonded by an adhesive agent.
[0014] Between the functional transparent plate and the first
.lamda./4 retarder, spaces may be formed due to a surface structure
of either of a bottom surface of the functional transparent plate
or a top surface of the first .lamda./4 retarder, and these spaces
may be filled with a filling material with a refractive index that
is equal to an average of refractive indices of the functional
transparent plate and the first .lamda./4 retarder. As the filling
material for the spaces, an organic silicon-based material such as
silicon resin may be used.
[0015] The display panel assembly includes an LC layer. LC
molecules in the LC layer may be aligned in a 90.degree.-twisted
nematic (TN) mode, a vertical alignment (VA) mode, an electrically
controlled birefringence (ECB) mode, or an in-plane switching (IPS)
mode.
[0016] The top surface of the functional transparent plate may have
a plurality of prisms consisting of first facets, on which a
cholesteric liquid crystal layer does not exist, and second facets,
on which a cholesteric liquid crystal exists. In this case, the
first facets without the cholesteric liquid crystal material and
the second facets with the cholesteric liquid crystal material are
formed at the top surface of the functional transparent plate and
may reflect light once, respectively. As a result, the reflected
light is returned toward the first .lamda./4 retarder again.
[0017] The functional transparent plate may have a top and a bottom
surface with an embossed carving or a depressed carving pattern. At
this time, apexes formed in the patterns of the two surfaces may be
formed to deviate from one another.
[0018] According to another aspect of the present invention, there
is provided a display device including: a display panel assembly; a
first .lamda./4 retarder that is provided on the display panel
assembly; a reflective polarizer that is provided above the first
.lamda./4 retarder to transmit incident light which is linearly
polarized in a first direction and to reflect incident light which
is linearly polarized in a second direction perpendicular to the
first direction; a second .lamda./4 retarder that is provided on
the reflective polarizer; a functional transparent plate that is
provided on the second .lamda./4 retarder and which has a top
surface with first facets and second facets where the second facets
transmit only a component of incident light which is polarized in a
specific direction and reflect the remaining components; a third
.lamda./4 retarder that is provided under the display panel
assembly; and a lower polarizer that is provided under the third
.lamda./4 retarder.
[0019] The second facets that are formed at the top surface of the
functional transparent plate may have a cholesteric liquid crystal
layer thereon.
[0020] The display device may further include an upper polarizer
that is provided between the first .lamda./4 retarder and the
reflective polarizer.
[0021] The reflective polarizer may be a polarizer utilizing a dual
brightness enhancement film (DBEF) that is produced based on
reflectance anisotropy caused by refractive index anisotropy, or
delicate linear patterns.
[0022] The display device may further include a backlight unit that
is provided under the lower polarizer.
[0023] In this device, the functional transparent plate, the second
.lamda./4 retarder, the reflective polarizer, the first .lamda./4
retarder, the display panel assembly, the third .lamda./4 retarder,
and the lower polarizer may be bonded by an adhesive agent.
[0024] Spaces may be formed between the functional transparent
plate and the second .lamda./4 retarder, due to a surface structure
of either of a bottom surface of the functional transparent plate
or a top surface of the second .lamda./4 retarder, and the spaces
may be filled with a filling material with a refractive index that
is equal to an average of refractive indices of the functional
transparent plate and the second .lamda./4 retarder. As the filling
material for the spaces, an organic silicon-based material such as
silicon resin may be used.
[0025] The second facets which are formed at the top surface of the
functional transparent plate may only transmit either of a
right-handed circularly polarized component or a left-handed
circularly polarized component of incident light, while reflecting
the remaining components.
[0026] The top surface of the functional transparent plate may have
a prismatic structure including the first facets, on which a
cholesteric liquid crystal layer does not exist, and the second
facets, on which a cholesteric liquid crystal exists. In this case,
the first facet and the second facet may reflect light which is
incident from the second .lamda./4 retarder once, respectively. As
a result, the reflected light is returned toward the second
.lamda./4 retarder again.
[0027] The functional transparent plate may have a top surface and
a bottom surface with an embossed carving or a depressed carving
pattern. In this structure, apexes formed in the patterns of the
two surfaces may be formed to deviate from one another.
[0028] According to still another embodiment of the present
invention, there is provided a display device including: a display
panel assembly; a first .lamda./4 retarder that is provided on the
display panel assembly; a reflective polarizer that is provided
above the first .lamda./4 retarder to transmit incident light which
is linearly polarized in a first direction and to reflect incident
light which is linearly polarized in a second direction
perpendicular to the first direction; a second .lamda./4 retarder
that is provided on the reflective polarizer; and a functional
transparent plate that is provided on the second .lamda./4 retarder
and which has a top surface with first facets and second facets
where the second facets transmit only a component of incident light
which is polarized in a specific direction and reflect the
remaining components.
[0029] The second facets which are formed at the top surface of the
functional transparent plate may have a cholesteric liquid crystal
layer thereon. In addition, the second facets which are formed at
the top surface of the functional transparent plate may only
transmit either of a right-handed circularly polarized component or
a left-handed circularly polarized component of incident light,
while reflecting the remaining components.
[0030] The top surface of the functional transparent plate may have
a prismatic structure including the first facets, on which a
cholesteric liquid crystal layer does not exist, and the second
facets, on which a cholesteric liquid crystal exists.
[0031] The functional transparent plate may have a top surface and
a bottom surface with an embossed carving or a depressed carving
pattern. In this case, apexes formed in the patterns of the two
surfaces may be formed to deviate from one another.
[0032] The first facets and the second facets which are formed at
the top surface of the functional transparent plate may reflect
light which is incident from the second .lamda./4 retarder once,
respectively. As a result, the reflected light is returned toward
the second .lamda./4 retarder again.
[0033] Between the functional transparent plate and the second
.lamda./4 retarder, spaces may be formed due to a surface structure
of either of a bottom surface of the functional transparent plate
or a top surface of the second .lamda./4 retarder. In this case,
the spaces may be filled with a filling material with a refractive
index that is equal to an average of refractive indices of the
functional transparent plate and the second .lamda./4 retarder. As
the filling material for the spaces, an organic silicon-based
material, such as silicon resin or the like, may be used.
[0034] According to still another embodiment of the present
invention, there is provided a display device including: a display
panel assembly; a selective reflection layer that is provided above
the display panel assembly to transmit a component of incident
exterior light which is circularly polarized in a first direction
and to reflect a component of incident exterior light which is
circularly polarized in a second direction perpendicular to the
first direction; and a functional transparent plate that is
provided on the selective reflection layer and which has a top
surface including portions without a cholesteric liquid crystal
material and portions with a cholesteric liquid crystal
material.
[0035] The display device may further include a first polarizer
that is provided between the selective reflection layer and the
display panel assembly, a first .lamda./4 retarder that is provided
between the first polarizer and the display panel assembly, a
second .lamda./4 retarder that is provided between the selective
reflection layer and the first polarizer, a second polarizer that
is provided under the display panel assembly, a third .lamda./4
retarder that is provided between the second polarizer and the
display panel assembly, and a backlight unit that is provided under
the display panel assembly.
[0036] In this structure, the selective reflection layer may be
formed of a cholesteric liquid crystal material.
[0037] In this device, the display panel, the selective reflection
layer, and the functional transparent plate may be bonded using an
adhesive agent.
[0038] Spaces may be formed between the functional transparent
plate and the selective reflection layer, due to a surface
structure of either of a bottom surface of the functional
transparent plate or a top surface of the selective reflection
layer, and the spaces may be filled with a filling material with a
refractive index that is equal to an average of refractive indices
of the functional transparent plate and the selective reflection
layer. As the filling material for the spaces, an organic
silicon-based material such as silicon resin may be used.
[0039] The display panel assembly includes an LC layer. LC
molecules in the LC layer may be aligned in a 90.degree.-twisted
nematic (TN) mode, a vertical alignment (VA) mode, an electrically
controlled birefringence (ECB) mode, or an in-plane switching (IPS)
mode.
[0040] The top surface of the functional transparent plate may have
a plurality of prisms consisting of first facets, on which a
cholesteric liquid crystal layer does not exist, and second facets,
on which a cholesteric liquid crystal exists. In this structure,
the first facets and the second facets formed at the top surface of
the functional transparent plate may reflect light which is
incident from the selective reflection layer once, respectively. As
a result, the reflected light is returned toward the selective
reflection layer again.
[0041] The functional transparent plate may have a top surface and
a bottom surface with an embossed carving or a depressed carving
pattern. In this case, apexes formed in the patterns of the two
surfaces may be formed to deviate from one another.
[0042] According to still another embodiment of the present
invention, there is provided a display device including: a display
panel assembly; a first .lamda./4 retarder that is provided on the
display panel assembly; a first polarizer that is provided on the
first .lamda./4 retarder where the first polarizer transmits
external incident light which is linearly polarized in a first
direction and that reflects external incident light which is
linearly polarized in a second direction perpendicular to the first
direction; a second .lamda./4 retarder that is provided on the
first polarizer; a selective reflection layer that is provided on
the second .lamda./4 retarder to transmit a component of incident
light which is circularly polarized in a third direction and to
reflect a component of incident light which is circularly polarized
in a fourth direction that is perpendicular to the third direction;
a functional transparent plate that is provided on the selective
reflection layer and which has a top surface with first facets and
second facets where the second facets transmit only a component of
incident light which is polarized in a specific direction and
reflect the remaining components; a third .lamda./4 retarder that
is provided under the display panel assembly; and a second
polarizer that is provided under the third .lamda./4 retarder.
[0043] In this structure, the second facets which are formed at the
top surface of the functional transparent plate may have a
cholesteric liquid crystal layer thereon, and the selective
reflection layer may be formed of a cholesteric liquid crystal
material.
[0044] The display device may further include a backlight unit that
is provided under the second polarizer.
[0045] In this device, the functional transparent plate, the
selective reflection layer, the second .lamda./4 retarder, the
first polarizer, the first .lamda./4 retarder, the display panel
assembly, the third .lamda./4 retarder, and the second polarizer
may be bonded by an adhesive agent.
[0046] Between the functional transparent plate and the selective
reflection layer, spaces may be formed due to a surface structure
of either of a bottom surface of the functional transparent plate
or a top surface of the selective reflection layer. These spaces
may be filled with a filling material with a refractive index that
is equal to an average of refractive indices of the functional
transparent plate and the selective reflection layer. As the
filling material for the spaces, an organic silicon-based material
such as silicon resin may be used.
[0047] The second facets which are formed at the top surface of the
functional transparent plate may only transmit either of a
right-handed circularly polarized component or a left-handed
circularly polarized component of incident light, while reflecting
the remaining components.
[0048] The top surface of the functional transparent plate may have
a prismatic structure including the first facets, on which a
cholesteric liquid crystal layer does not exist, and the second
facets, on which the cholesteric liquid crystal exists. In this
case, the first facets and the second facets which are formed at
the top surface of the functional transparent plate may reflect
light which is incident from the selective reflection layer once,
respectively. As a result, the reflected light is returned toward
the selective reflection layer again.
[0049] The functional transparent plate may have a top surface and
a bottom surface with an embossed carving or a depressed carving
pattern. In this case, apexes formed in the patterns of the two
surfaces may be formed to deviate from one another.
[0050] According to still another embodiment of the present
invention, there is provided a display device including: a display
panel assembly; a first .lamda./4 retarder that is provided on the
display panel assembly; a first polarizer that is provided on the
first .lamda./4 retarder where the first polarizer transmits light
which is linearly polarized in a first direction and reflects light
which is linearly polarized in a second direction perpendicular to
the first direction; a second .lamda./4 retarder that is provided
on the first polarizer; a selective reflection layer that is
provided on the second .lamda./4 retarder to transmit light which
is circularly polarized in a third direction and to reflect light
which is circularly polarized in a fourth direction that is
opposite to the third direction; and a functional transparent plate
that is provided on the selective reflection layer and which has a
top surface with first facets and second facets where the second
facets transmit only light which is polarized in a specific
direction and reflect the remaining light.
[0051] The second facets which are formed at the top surface of the
functional transparent plate may have a cholesteric liquid crystal
layer thereon, and may only transmit either of a right-handed
circularly polarized component or a left-handed circularly
polarized component of incident light and reflect the remaining
components.
[0052] The top surface of the functional transparent plate may have
a prismatic structure including the first facets, on which a
cholesteric liquid crystal layer does not exist, and the second
facets, on which a cholesteric liquid crystal exists. In this case,
the first facets and the second facets which are formed at the top
surface of the functional transparent plate may reflect light which
is incident from the selective reflection layer once, respectively.
As a result, the reflected light is returned toward the selective
reflection layer again.
[0053] The functional transparent plate may have a top surface and
a bottom surface with an embossed carving or a depressed carving
pattern. In this case, apexes of the patterns of the two surfaces
may be formed to deviate from one another.
[0054] Spaces may be formed between the functional transparent
plate and the selective reflection layer, due to a surface
structure of either of a bottom surface of the functional
transparent plate or a top surface of the selective reflection
layer. These spaces may be filled with a filling material with a
refractive index that is equal to an average of refractive indices
of the functional transparent plate and the selective reflection
layer. As the filling material for the spaces, an organic
silicon-based material such as silicon resin may be used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] The above objects and other advantages of the present
invention will become more apparent by describing the preferred
embodiments thereof in more detail with reference to the
accompanying drawings.
[0056] FIG. 1 is a layout view of an LCD according to an embodiment
of the present invention.
[0057] FIG. 2 is a schematic cross-sectional view cut along II-II'
of FIG. 1.
[0058] FIG. 3 is a schematic cross-sectional view cut along
III-III' of FIG. 1.
[0059] FIG. 4 shows a vertical scheme of the LCD according to an
embodiment of the present invention.
[0060] FIG. 5 shows variations of the polarization state of light
at an upper portion of an LCD according to an embodiment of the
present invention.
[0061] FIG. 6 is a view for comparing the polarization states of
light when an LCD operates in a reflection mode utilizing exterior
light and in a transmission mode utilizing internal light.
[0062] FIG. 7 through FIG. 12 are schematic cross-sectional views
showing process steps to manufacture a functional transparent plate
of an LCD according to an embodiment of the present invention.
[0063] FIG. 13 is a schematic cross-sectional view of a functional
transparent plate of an LCD according to another embodiment of the
present invention.
[0064] FIG. 14 is a cross-sectional view showing variations of the
polarization state of light in a reflective LCD according to still
another embodiment of the present invention.
[0065] FIG. 15 is a layout view of an LCD according to still
another embodiment of the present invention.
[0066] FIG. 16 is a schematic cross-sectional view cut along
XVI-XVI' of FIG. 15.
[0067] FIG. 17 is a schematic cross-sectional view cut along
XVII-XVII' of FIG. 15.
[0068] FIG. 18 shows a vertical scheme of an LCD according to still
another embodiment of the present invention.
[0069] FIG. 19 shows variations of the polarization state of light
at an upper part of an LCD according to still another embodiment of
the present invention.
[0070] FIG. 20 is a view for comparing the polarization states of
light when an LCD operates in a reflection mode utilizing exterior
light and in a transmission mode utilizing internal light from a
backlight unit.
[0071] FIG. 21 through FIG. 24 are schematic cross-sectional views
showing process steps to manufacture a selective reflection layer
of an LCD according to still another embodiment of the present
invention.
[0072] FIG. 25 through FIG. 30 are schematic cross-sectional views
showing process steps to manufacture a functional transparent plate
of an LCD according to still another embodiment of the present
invention.
[0073] FIG. 31 is a schematic cross-sectional view of a functional
transparent plate of an LCD according to still another embodiment
of the present invention.
[0074] FIG. 32 is a cross-sectional view showing variations of the
polarization state of light in a reflective LCD according to still
another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0075] Preferred embodiments of the present invention will now be
described more fully hereinafter with reference to the accompanying
drawings, in which preferred embodiments of the invention are
shown. The present invention may, however, be embodied in different
forms and should not be construed as being limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in
the art.
[0076] In the drawings, the thickness of the layers, films, and
regions are exaggerated for clarity. Like numerals refer to like
elements throughout. It will be understood that when an element
such as a layer, film, region, or substrate is referred to as being
"on" another element, it can be directly on the other element or
intervening elements may also be present.
[0077] Hereinafter, an LCD according to a preferred embodiment of
the present invention will be described in detail with reference to
FIG. 1 through FIG. 3.
[0078] FIG. 1 is a layout view of an LCD according to an embodiment
of the present invention, and FIG. 2 and FIG. 3 are schematic
cross-sectional views cut along II-II' and III-III' of FIG. 1,
respectively.
[0079] Referring to FIG. 1 to FIG. 3, the LCD of this embodiment
includes a TFT array panel 100 and a common electrode panel 200
facing each other, and an LC layer 3 that is interposed
therebetween with LC molecules that are aligned perpendicular or
parallel to the surfaces of the two panels 100 and 200.
[0080] LC molecules in the LC layer 3 are aligned in a
90.degree.-twisted nematic (TN) mode, a vertical alignment (VA)
mode, or an electrically controlled birefringence (ECB) mode.
[0081] The TFT array panel 100 is configured as follows.
[0082] A plurality of gate lines 121 and a plurality of storage
electrode lines 131 are formed on an insulating substrate 110 made
of transparent glass or plastic.
[0083] The gate lines 121 for transmitting gate signals extend
substantially in a horizontal direction, while being separated from
each other. Each gate line 121 includes a plurality of gate
electrodes 124 protruding upward and an end portion 125 having a
relatively large dimension to be connected to an external
device.
[0084] The storage electrode lines 131 extend substantially in a
horizontal direction and are substantially parallel to the gate
lines 121. Each storage electrode line 131 includes a plurality of
storage electrodes 133 protruding upward and downward. The storage
electrode lines 131 receive a predetermined voltage, such as a
common voltage that is applied to a common electrode 270 of the
common electrode panel 200.
[0085] The gate lines 121 and the storage electrode lines 131 are
preferably made of an aluminum (Al) containing metal such as Al and
an Al alloy, a silver-(Ag) containing metal such as Ag and a Ag
alloy, a copper-(Cu) containing metal such as Cu and a Cu alloy, a
molybdenum-(Mo) containing metal such as Mo and a Mo alloy, chrome
(Cr), titanium (Ti), or tantalum (Ta). The gate lines 121 and the
storage electrode lines 131 may be configured as a multi-layered
structure, in which at least two conductive layers (not shown)
having different physical properties are included. In such a
structure, an upper layer of the two is made of a low resistivity
metal, such as an Al-containing metal, an Ag-containing metal, a
Cu-containing metal, or the like, in order to reduce delay of the
signals or a voltage drop in the gate lines 121 and the storage
electrode lines 131, and a lower layer is made of material having
prominent physical, chemical, and electrical contact properties
with other materials such as indium tin oxide (ITO), indium zinc
oxide (IZO), etc. For example, a Mo-containing metal, Cr, Ta, or
Ti, etc., may be used for the formation of the same layer. A
desirable example of the combination of the two layers is a lower
Cr layer and an upper Al--Nd layer. However, the gate lines 121 and
the storage electrode lines 131 may be configured as single-layered
structures.
[0086] All lateral sides of the gate lines 121 and the storage
electrode lines 131 preferably slope in a range from about
20.degree. to 80.degree. to the surface of the substrate 110.
[0087] A gate insulating layer 140 made of silicon nitride
(SiN.sub.x) or silicon oxide (SiO.sub.2) is formed on the gate
lines 121 and the storage electrode lines 131.
[0088] A plurality of linear semiconductors 151 made of
hydrogenated amorphous silicon (abbreviated as "a-Si") or
polysilicon are formed on the gate insulating layer 140. Each
linear semiconductor 151 extends substantially in a vertical
direction and includes a plurality of projections 154 that extend
along the respective gate electrodes 124 and a plurality of
extensions 157 that extend from the respective projections 154. The
linear semiconductors 151 are enlarged in the vicinities of the
gate lines 121 and the storage electrode lines 131 to cover them
entirely.
[0089] A plurality of linear ohmic contacts 161 and island-shaped
ohmic contacts 165 are formed on the linear semiconductors 151. The
ohmic contacts 161 and 165 may be made of N+ hydrogenated amorphous
silicon that is highly doped with N-type impurities, or silicide.
The linear ohmic contacts 161 include a plurality of projections
163. A set of a projection 163 and an island-shaped ohmic contact
165 is placed on the projection 154 of the semiconductor 151.
[0090] All lateral sides of the semiconductors 151 and the ohmic
contacts 161 and 165 slope in the range from about 20.degree. to
80.degree. to the surface of the substrate 110.
[0091] A plurality of data lines 171 and a plurality of drain
electrodes 175, separated from the data lines 171, are formed on
the ohmic contacts 161 and 165 and the gate insulating layer
140.
[0092] The data lines 171 for transmitting data signals extend
substantially in a vertical direction to be crossed with the gate
lines 121 and the storage electrode lines 131. Each data line 171
includes an end portion 179 having a relatively large dimension to
be connected to a different layer or an external device.
[0093] Each drain electrode 175 includes an expansion 177 that is
overlapped with one of the storage electrodes 133. Each data line
171 further includes a plurality of source electrodes 173
protruding along and extending toward the respective gate
electrodes 124. Each source electrode 173 surrounds a partial
portion of a bar-shaped end portion of the drain electrode 175.
[0094] A gate electrode 124, a source electrode 173, a drain
electrode 175, and a projection 154 of the semiconductor 151 form a
thin film transistor (TFT). A TFT channel is formed in the
projection 154 provided between the source electrode 173 and the
drain electrode 175.
[0095] The data lines 171 and the drain electrodes 175 are
preferably made of a refractory metal, such as a Mo-containing
metal, a Cr-containing metal, Ta, Ti, or the like, and may be
configured as multi-layered structures including a lower layer (not
shown) consisting of one among Mo, a Mo alloy, Cr, etc., and an
upper layer (not shown) consisting of an Al-containing metal.
[0096] Similarly to the gate lines 121 and the storage electrode
lines 131, all lateral sides of the data lines 171 and the drain
electrodes 175 slope in the range from about 20.degree. to
80.degree. to the surface of the substrate 110.
[0097] The ohmic contacts 161 and 165 exist only between the
underlying semiconductors 151 and the overlying data lines 171 and
between the overlying drain electrodes 175 and the underlying
semiconductors 151, in order to reduce contact resistance
therebetween. The linear semiconductors 151 are partially exposed
at places where the data lines 171 and the drain electrodes 175 do
not cover them, as well as between the source electrodes 173 and
the drain electrodes 175.
[0098] A passivation layer 180, made of an inorganic material such
as SiN.sub.x or SiO.sub.2, is formed on the data lines 171, the
drain electrodes 175, and the exposed portions of the
semiconductors 151.
[0099] An organic insulating layer 187, made of a photosensitive
organic insulator having a prominent planarization property, is
formed on the passivation layer 180. A top surface of the organic
insulating layer 187 is uneven. Due to the uneven surface,
reflective electrodes 194 overlying the organic insulating layer
187 have uneven top surfaces. The uneven top surfaces of the
reflective electrodes 194 prevent mirror reflection. Accordingly,
images that may be shown on an LCD screen due to the mirror
reflection are eliminated. The organic insulating layer 187 is
removed at the end portions 125 and 179 of the gate lines 121 and
the data lines 171, so only the passivation layer 180 remains on
the end portions 125 and 179.
[0100] The passivation layer 180 is provided with a plurality of
contact holes 183, through which the end portions 179 of the data
lines 171 are exposed. A plurality of contact holes 182 are formed
in the passivation layer 180 and the gate insulating layer 140, and
the end portions 125 of the gate lines 121 are exposed
therethrough. A plurality of contact holes 185 are formed in the
passivation layer 180 and the organic insulating layer 187, and the
expansions 177 of the drain electrodes 175 are exposed
therethrough. The contact holes 182, 183, and 185 may have
polygonal or circular shapes. The sidewalls of the contact holes
182, 183, and 185 slope in the range from about 30.degree. to
85.degree. to the surface of the substrate 110 or are shaped as
steps.
[0101] A plurality of pixel electrodes 190 are formed on the
organic insulating layer 187.
[0102] Each pixel electrode 190 includes a transparent electrode
192 and a reflective electrode 194 overlying the transparent
electrode 192. The transparent electrodes 192 are made of a
transparent conductive material such as ITO or IZO, and the
reflective electrodes 194 are made of a reflective opaque material
such as Al, an Al alloy, Ag, or an Ag alloy. Each pixel electrode
190 may further include a contact assistant (not shown) made of Mo,
a Mo alloy, Cr, Ti, or Ta. The contact assistants ensure contact
properties between the transparent electrodes 192 and the
reflective electrodes 194, while preventing the transparent
electrodes 192 from oxidizing the reflective electrodes 194.
[0103] Each pixel is divided into a transmission area TA without
the reflective electrode 194 and a reflection area RA with the
reflective electrode 194. The organic insulating layer 187 is
removed from the transmission area TA, so that a transmission
window 195 is formed there. Due to the transmission window 195, a
cell gap of the transmission area TA becomes nearly twice as large
as that of the reflection area RA, so that a light path difference
between the transmission area TA and the reflection area RA is
compensated.
[0104] The pixel electrodes 190 are physically and electrically
connected to the expansions 177 of the drain electrodes 175 through
the contact holes 185 to receive data voltages from the drain
electrodes 175. The pixel electrodes 190 are supplied with the data
voltages to generate electric fields in cooperation with the common
electrode 270 of the common electrode panel 200, determining the
molecular orientation of the LC layer 3 interposed between the two
electrodes.
[0105] Each set of the pixel electrode 190 and the common electrode
270 forms an LC capacitor that is capable of storing the applied
voltage after the TFT is turned off. To enhance the voltage storage
ability of the LC capacitors, storage capacitors, connected to the
LC capacitors in parallel, are further provided. Overlapping of the
expansions 177 of the drain electrodes 175 with the storage
electrodes 133 implements the storage capacitors. Otherwise,
overlapping of the pixel electrodes 190 with the gate lines 121
adjacent thereto may implement the storage capacitors. In this
case, the storage electrode lines 131 may be omitted.
[0106] The pixel electrodes 190 may be overlapped with the data
lines 171 adjacent thereto as well as the gate lines 121 adjacent
thereto, in order to increase the aperture ratio, but such overlap
portions are not always necessary.
[0107] The pixel electrodes 190 may be made of a transparent
conductive polymer. However, opaque reflective metals may be used
in reflective LCDs.
[0108] A plurality of contact assistants 95 and 97 are formed on
the passivation layer 180 relating to a pad portion, and are
individually connected to the end portions 125 of the gate lines
121 and the end portions 179 of the data lines 171 through the
contact holes 182 and 183. The contact assistants 95 and 97
supplement adhesion between the end portions 125 and 179 and
exterior devices, and protect them. The contact assistants 95 and
97 may be formed on the same layer as the transparent electrodes
192 or the reflective electrodes 194. However, they may be omitted
because they are not essential elements.
[0109] The common electrode panel 200 facing the TFT array panel
100 is configured as follows.
[0110] A light-blocking member 220 called a "black matrix" is
provided on an insulating substrate 210 made of a transparent
insulating material such as glass. The light-blocking member 220
prevents light from leaking out through barriers between the pixel
electrodes 190 and delimits aperture regions facing the pixel
electrodes 190.
[0111] A plurality of color filters 230 are formed on the substrate
210 and the light-blocking member 220, and most of them are placed
within the aperture regions delimited by the light-blocking member
220. Each color filter 230 is formed between the two adjacent data
lines 171 in a vertical direction, and exhibits one among red,
green, and blue colors. The color filters 230 are connected to one
another in the form of stripes.
[0112] In the case of a typical transflective LCD, in the
transmission areas TA, light passes through the color filters 230
only once, while it passes twice in the reflection areas RA.
Accordingly, a difference of color tone between the transmission
areas TA and the reflection areas RA is generated. To reduce the
difference of color tone between the two areas TA and RA, two
methods can be used. The first method is to form the thickness of
each color filter 230 differently depending on its location. That
is, in this method, a specific portion of the color filter 230,
which is placed at the transmission area TA, is formed thicker than
the remaining portion, which is placed at the reflection area RA.
The second method is to form light holes in the reflection areas RA
of the color filters 230.
[0113] The common electrode 270, made of a transparent conductive
material such as ITO or IZO, is formed on the light-blocking member
220 and the color filters 230.
[0114] The LC layer 3 is interposed between the two panels 100 and
200 facing each other.
[0115] A lower polarizer 12 and an upper polarizer 22 are
individually attached to the outer surfaces of the two panels 100
and 200. A transmission axis (.theta.) of the upper polarizer 22
and a transmission axis (.theta.+90.degree.) of the lower polarizer
12 are mutually crossed at a right angle.
[0116] A lower .lamda./4 retarder 13 is interposed between the TFT
array panel 100 and the lower polarizer 12, and a first upper
.lamda./4 retarder 14 is interposed between the common electrode
panel 200 and the upper polarizer 22.
[0117] A reflective polarizer 15 is disposed on the upper polarizer
22, and a second upper .lamda./4 retarder 16 is disposed on the
reflective polarizer 15.
[0118] A functional transparent plate 17 is disposed on the second
upper .lamda./4 retarder 16. A top surface of the functional
transparent plate 17 consists of a plurality of prisms. Each prism
includes a first facet 17-1 on which no additional material exists
and a second facet 17-2 on which a cholesteric LC layer exists.
[0119] Hereinafter, the structure of the above-mentioned LCD and
the polarization principles of light in the same LCD will be
described in detail.
[0120] FIG. 4 shows a vertical scheme of the LCD of an embodiment
of the present invention.
[0121] A display panel assembly 300 of FIG. 4 comprises the TFT
array panel 100 and the common electrode panel 200, and the LC
layer 3 interposed therebetween.
[0122] The lower .lamda./4 retarder 13 is attached to a lower
surface of the display panel assembly 300, and the lower polarizer
12 is attached to a lower surface of the lower .lamda./4 retarder
13.
[0123] Meanwhile, the first upper .lamda./4 retarder 14 is attached
to an upper surface of the display panel assembly 300, and the
upper polarizer 22 is attached to an upper surface of the first
upper .lamda./4 retarder 14. The reflective polarizer 15 is
attached to an upper surface of the upper polarizer 22 and the
second upper .lamda./4 retarder 16 is attached onto the reflective
polarizer 15. The functional transparent plate 17, whose top
surface consists of a plurality of combinations of the first facet
17-1 and second facet 17-2, is formed on the second upper .lamda./4
retarder 16.
[0124] A more detailed description for the above-discussed
structure is given below.
[0125] The polarizers 12 and 22 are individually attached to the
outer surfaces of the panels 100 and 200. Their transmission axes
are mutually crossed at a right angle. The two polarizers 12 and 22
are absorption-type polarizers that transmit linearly polarized
incident light vibrating parallel to their transmission axes and
absorb linearly polarized incident light vibrating perpendicular to
their transmission axes.
[0126] The LCD of this embodiment utilizes three .lamda./4
retarders in total. Each of the three .lamda./4 retarders 13, 14,
and 16 converts circularly polarized light into linearly polarized
light or linearly polarized light into circularly polarized light
by causing a phase difference of a quarter wavelength between two
polarized components that are orthogonal to each other and are
individually parallel to a fast axis and a slow axis thereof. Here,
the circularly polarized light may be elliptically polarized light
in actuality, but the elliptically polarized light will also be
referred to as circularly polarized light for convenience.
[0127] The fast axes of the three .lamda./4 retarders 13, 14, and
16 are preferably formed at .+-.45.degree. to the transmission axes
(.theta. and .theta.+90.degree.) of the polarizers 12 and 22 to
maximize the phase difference between the two polarized components.
However, they may be disposed at different angles, except being
disposed perpendicular or parallel to each other.
[0128] The reflective polarizer 15 is disposed on the upper
polarizer 22. A transmission axis and a reflection axis of the
reflective polarizer 15 are mutually perpendicular. Accordingly,
the reflective polarizer 15 transmits linearly polarized incident
light that vibrates parallel to the transmission axis, while
reflects linearly polarized incident light that vibrates parallel
to the reflection axis. The reflective polarizer 15 is formed of a
dual brightness enhancement film (DBEF), as disclosed in U.S. Pat.
No. 5,825,543, utilizing the reflectance anisotropy caused by the
refractive index anisotropy. Otherwise, the reflective polarizer 15
may utilize delicate linear patterns disclosed by Japanese Patent
Publication No. 1990-308166. The transmission axes of the
reflective polarizer 15 and the upper polarizer 22 are disposed in
the same direction.
[0129] The functional transparent plate 17 is made of a transparent
material and has a prismatic top surface consisting of a plurality
of first facets 17-1 and a plurality of second facets 17-2, as
shown in FIG. 4. No additional material exists on the first facets
17-1, while the cholesteric LC layer exists on the second facets
17-2. The second facets 17-2 transmit circularly polarized incident
light rotating in the same direction as an optical axis of the
cholesteric LC layer, while reflecting circularly polarized
incident light rotating in an opposite direction. A fabrication
method of the first facets 17-1 and the second facets 17-2 will be
described later.
[0130] The functional transparent plate 17, the second upper
.lamda./4 retarder 16, the reflective polarizer 15, the upper
polarizer 22, the first upper .lamda./4 retarder 14, the display
panel assembly 300, the lower .lamda./4 retarder 13, and the lower
polarizer 12 are bonded by an adhesive agent in that order.
[0131] FIG. 5 shows variations of the polarization state of light
at an upper part of the LCD with the functional transparent plate
17, the second upper .lamda./4 retarder 16, the reflective
polarizer 15, and the upper polarizer 22.
[0132] As shown in FIG. 5, light, which is incident onto the
functional transparent plate 17, is classified into three light
rays (A, B, and C) depending on incident position and incident
angle.
[0133] First, incident light (A) of the three light rays is
described.
[0134] The light (A), which is incident onto the second facets 17-2
of the functional transparent plate 17, is separated into two
individual light rays (A-1) and (A-2) having different light paths
from each other. That is, when the light (A) impacts the second
facets 17-2 where the cholesteric LC layer is formed, only
right-handed circularly polarized light (A-1) of the incident light
(A), which rotates in the same direction as the optical axis of the
cholesteric LC layer, passes through the functional transparent
plate 17, while left-handed circularly polarized light (A-2), which
rotates in the opposite direction, is reflected.
[0135] The light (A-1) passing through the transparent plate 17
then travels through the second upper .lamda./4 retarder 16. At
this time, the light (A-1) is converted into light that is linearly
polarized in the X direction. Next, the linearly polarized light
(A-1) sequentially passes through the reflective polarizer 15 and
the upper polarizer 22. In this structure, the transmission axis of
the upper polarizer 22 is in the X-direction, while the reflection
axis of the reflective polarizer 15 is in the Y-direction.
[0136] Meanwhile, the left-handed circularly polarized reflected
light (A-2) passes through the first facets 17-1 and is then
reflected again by an adjacent second facet 17-2. The polarization
state of the light (A-2) is maintained with no change during these
sequential processes. This is possible because the second facets
17-2 that are formed with the cholesteric LC do not cause any
change in the polarization state of the light when reflecting it.
Next, the left-handed circularly polarized light (A-2) enters the
second upper .lamda./4 retarder 16. At this time, the second upper
.lamda./4 retarder 16 converts the incident light (A-2) into
linearly polarized light in the Y direction. Then, the linearly
polarized light (A-2) is returned back by the reflective polarizer
15 because the reflection axis of the reflective polarizer 15 and
the polarized direction of the light (A-2) are in the same
direction. The light that is reflected by the reflective polarizer
15 is designated as (A-3) in FIG. 5.
[0137] Incident light (B) of FIG. 5 is described below.
[0138] The light (B), which is incident onto the first facets 17-1
of the functional transparent plate 17, passes though the
functional transparent plate 17 and the second upper .lamda./4
retarder 16. Even after passing through the second upper .lamda./4
retarder 16, the light (B) includes all-directional components
without a change. In other words, the second upper .lamda./4
retarder 16 transmits all components of the incident light (B).
Next, the light (B) enters the reflective polarizer 15, which
allows only those components of the light that are parallel to its
transmission axis (i.e., the X direction) to pass and reflects the
components perpendicular to the transmission axis. Accordingly, the
light (B) is divided into two separate light rays (B-1) and (B-2)
by the reflective polarizer 15.
[0139] Meanwhile, light (C), which is perpendicularly incident to
the second facets 17-2 of the functional transparent plate 17, is
also divided into two separate light rays (C-1) and (C-2) having
different light paths. That is, a right-handed circularly polarized
component (C-1) of the incident light (C), which rotates in the
same direction as the optical axis of the cholesteric LC layer,
passes through the functional transparent plate 17 and then
proceeds along the same light path as the light (A-1), while a
left-handed circularly polarized component (C-2) of the incident
light (C), which rotates in the opposite direction, exits the LCD
by reflection at the second facets 17-2. Here, plane angles of the
first facets 17-1 and the second facets 17-2 may be controlled so
that the left-handed circularly polarized reflected light (C-2) is
incident onto the first facets 17-1 again and then enters the
second upper .lamda./4 retarder 16 after being reflected or
refracted by the functional transparent plate 17.
[0140] In the meantime, the linearly polarized light rays (A-3) and
(B-2), which are reflected by the reflective polarizer 15, enter
the second upper .lamda./4 retarder 16 again. At this time, the
second upper .lamda./4 retarder 16 converts the incident light
(A-3) and (B-2) into left-handed circularly polarized light (D).
The left-handed circularly polarized light (D) is divided into two
light rays (D-1) and (D-2) depending on incident positions of the
light (D). That is, the light (D-1) is incident onto the first
facets 17-1 of the functional transparent plate 17, while the light
D-2 is incident onto the second facets 17-2. The two light rays
(D-1) and (D-2) are doubly reflected by the first facets 17-1 and
the second facets 17-2, respectively. At this time, the light rays
(D-1) and (D-2) undergo 180.degree. phase changes with the
reflection at the first facets 17-1, so that they are all converted
into right-handed polarized light rays. Next, the right-handed
polarized light rays (D-1) and (D-2) enter the second upper
.lamda./4 retarder 16 again, and the second upper .lamda./4
retarder 16 transmits the incident light rays (D-1) and (D-2),
converting them into linearly polarized light rays in the X
direction, in a similar manner to the light (A-1).
[0141] As described above, the light, which is incident from the
ambient environment through the first facets 17-1 and the second
facets 17-2 of the functional transparent plate 17, does not exit
the LCD after being reflected by the reflective polarizer 15 and is
returned to the reflection polarizer 15 again by changing its
polarization direction, so that display luminance of the LCD in a
reflection mode is improved. To accomplish this effect, it is
preferable to design the functional transparent plate 17 so that
the first facets 17-1 and the second facets 17-2 thereof represent
the largest possible refractive index difference, while having the
largest possible dimensions. It is also preferable to form angles
between the two facets 17-1 and 17-2 to be large and as far as
possible. In the case that the difference between the refractive
indices of the exterior air and the functional transparent plate 17
is large, no total reflection occurs when exterior light enters the
functional transparent plate 17, but a total reflection occurs when
the light is emitted from the functional transparent plate 17.
Accordingly, utilization efficiency for the exterior light is
improved.
[0142] FIG. 6 is a view for comparing the polarization states of
light when the LCD operates in a reflection mode utilizing exterior
light and in a transmission mode utilizing internal light.
[0143] In this embodiment, the LC layer 3 consists of twisted
nematic LC molecules. The twisted nematic LC molecules have
peculiar optical properties. In detail, they are aligned in a
vertical direction when an electric field is applied, thereby
causing no change in the polarization state of light passing
through the LC layer 3, but they are alighted in a horizontal
direction when no electric field is applied, thereby changing the
polarization state of light passing through the LC layer 3.
[0144] Hereinafter, variations of the polarization states of light
when no electric field is applied to the LC layer 3 will be first
described with reference to FIG. 6.
[0145] In FIG. 6, leftmost light (R1) is incident light from the
ambient environment when no electric field is applied to the LC
layer 3 in a reflection mode. The light (R1) successively passes
through the reflective polarizer 15 and the upper polarizer 22 as
linearly polarized light in the X direction. The linearly polarized
light (R1) then enters the first upper .lamda./4 retarder 14. At
this time, the first upper .lamda./4 retarder 14 converts the
incident light into right-handed circularly polarized light. The
right-handed circularly polarized light (R1) enters the LC layer 3
after passing through the upper insulating substrate 210 and the
color filters 230. In this case, since the LC layer 3 is supplied
with no electric field, the light is converted into linearly
polarized light in the Y direction. The linearly polarized light
(R1) rotates by 180.degree. with the reflection at the reflective
polarizer 15. However, the light (R1) maintains the polarization
state without a change even after rotation. The reflected light
(R1) is converted into right-handed circularly polarized light
again when passing through the LC layer 3, and then enters the
first upper .lamda./4 retarder 14 after passing through the color
filters 230 and the upper insulating substrate 210. At this time,
the first upper .lamda./4 retarder 14 converts the right-handed
circularly polarized light (R1) into linearly polarized light in
the X direction. Next, the linearly polarized light (R1) enters the
second upper .lamda./4 retarder 16 after passing through the upper
polarizer 22 and the reflective polarizer 15. At this time, the
linearly polarized light (R1) is converted into right-handed
circularly polarized light by the second upper .lamda./4 retarder
16 and then exits the LCD after passing through the functional
transparent plate 17. At this time, the LCD screen is shown as a
white state.
[0146] Meanwhile, light is supplied from an internal light source,
i.e., a backlight unit 500. The light passes through the lower
polarizer 12. In this step, only a linearly polarized component of
the light (T) in the Y direction remains and the remaining
components are removed by absorption. The linearly polarized
component (T) is converted into left-handed circularly polarized
light (T1, T2) by the lower .lamda./4 retarder 13. Light (T1) is
light supplied from the internal light source when no electric
field is applied to the LC layer 3 in a transmission mode The
left-handed circularly polarized light (T1) enters the LC layer 3
after passing through the lower insulating substrate 110, and is
converted into right-handed circularly polarized light when passing
through the LC layer 3. The right-handed circularly polarized light
(T1) passes through the upper insulating substrate 210 and then
enters the first upper .lamda./4 retarder 14. At this time, the
light (T1) is converted into linearly polarized light in the X
direction by the first upper .lamda./4 retarder 14. Next, the
linearly polarized light (T1) successively passes through the upper
polarizer 22 and the reflective polarizer 15. Then, the light (T1)
passing though the two polarizers passes thought the second upper
.lamda./4 retarder 16, thereby being converted into right-handed
circularly polarized light. The right-handed circularly polarized
light (T1) then exits the LCD. At this time, the LCD screen is
shown as a white state.
[0147] Hereinafter, variations of the polarization states in the
case of the field-applied LC layer 3 will be discussed with
reference to FIG. 6.
[0148] In FIG. 6, light (R2) is incident light from the ambient
environment when an electric field is applied to the LC layer 3 in
a reflection mode. The light (R2) successively passes through the
reflective polarizer 15 and the upper polarizer 22 as linearly
polarized light in the X direction. The linearly polarized light
(R2) then enters the first upper .lamda./4 retarder 14. At this
time, the first upper .lamda./4 retarder 14 converts the incident
light (R2) into right-handed circularly polarized light. Next, the
right-handed circularly polarized light (R2) enters the LC layer 3
after passing through the upper insulating substrate 210 and the
color filters 230. In this case, the field-applied LC layer 3 does
not cause a change in the polarization state of the light passing
therethrough. Sequentially, the right-handed circularly polarized
light (R2) rotates by 180.degree. with the reflection at the
reflective electrodes 194, thereby being converted into left-handed
circularly polarized light. The left-handed circularly polarized
light (R2), reflected by the reflective electrodes 194, passes
through the LC layer 3 again without a change of the polarization
state, and then enters the first upper .lamda./4 retarder 14 after
passing through the color filters 230 and the upper insulating
substrate 210. At this time, the first upper .lamda./4 retarder 14
converts the incident left-handed circularly polarized light (R2)
into linearly polarized light in the Y direction. Next, the upper
polarizer 22 completely absorbs linearly polarized light in the Y
direction, so that no light exits the LCD. In this case, the LCD
screen is shown as a black state.
[0149] Meanwhile, light (T2) of FIG. 6 is light supplied from the
backlight unit 500 when an electric field is applied to the LC
layer 3 in a transmission mode. The light supplied from the
backlight unit 500 passes through the lower polarizer 13. In this
step, only a linearly polarized component (T) in the Y direction of
the light remains and the remaining components are removed by
absorption. The linearly polarized component in the Y direction is
converted into left-handed circularly polarized light by the lower
.lamda./4 retarder 13. The left-handed circularly polarized light
(T2) enters the LC layer 3 after passing through the lower
insulating substrate 110, and then exits the LC layer 3 with no
change of the polarization state. Next, the left-handed circularly
polarized light (T2) passes through the color filters 230 and the
upper insulating substrate 210, and then enters the first upper
.lamda./4 retarder 14. At this time, the light (T2) is converted
into linearly polarized light in the Y direction by the first upper
.lamda./4 retarder 14. Next, the upper polarizer 22 completely
absorbs the linearly polarized light (T2), so that no light exits
the LCD. In this case, the LCD screen is shown as a black
state.
[0150] As described above, regardless of the operation modes of the
LCD, the LCD screen exhibits the black state when the field is
applied to the LC layer 3, while exhibiting the white state when
the field is not applied to the LC layer 3.
[0151] FIG. 7 through FIG. 12 are schematic cross-sectional views
showing process steps to manufacture a functional transparent plate
17 of an LCD according to a preferred embodiment of the present
invention.
[0152] The functional transparent plate 17 is manufactured as
follows.
[0153] As shown in FIG. 7, the functional transparent plate 17 with
a prismatic top surface, which consists of first facets 17-1 and
second facets 17-2, is first formed, and then an optical alignment
agent 20 is coated thereon. The resultant structure of FIG. 7 is
then selectively exposed to light through a first mask 30 as shown
in FIG. 8. After exposure, as shown in FIG. 9, a development
process is performed so that an optical alignment layer 21 remains
only on the first facets 17-1. Subsequent to the development, a
cholesteric LC material 40 is coated on the functional transparent
plate 17, as shown in FIG. 10. Next, the resultant structure of
FIG. 10 is selectively exposed to light through a second mask 35 as
shown in FIG. 11. Then, as shown in FIG. 12, a development process
and a UV curing process are successively performed, so that a
cholesteric LC layer 41 is formed only on the second facets 17-2.
As a result, each second facet 17-2 consists of the optical
alignment layer 21 and the cholesteric LC layer 41.
[0154] FIG. 13 is a schematic cross-sectional view of a functional
transparent plate of an LCD according to still another embodiment
of the present invention.
[0155] Referring to FIG. 13, the functional transparent plate 17 of
this embodiment has a top surface with first facets 17-1 and second
facets 17-2 that are inwardly formed from the surface, and a
prismatic bottom surface that is similar to the top surface of the
functional transparent plate 17 of the previous embodiment. In this
structure, it is preferable that first apexes P1 and second apexes
P3 of the prismatic bottom surface and third apexes P2 of the top
surface are positioned on different vertical lines from each other.
This is because such a structure enables much of the reflected
light to reach the cholesteric LC layer of the second facets 17-2,
thus improving utilization efficiency of the light.
[0156] In this structure, an important problem is how to attach the
functional transparent plate 17 with the prismatic bottom surface
onto the second upper .lamda./4 retarder 16. Two possible methods
are discussed below.
[0157] The first method is to directly form the second upper
.lamda./4 retarder 16 on the bottom surface of the functional
transparent plate 17. In this case, the second upper .lamda./4
retarder 16 is shaped as the bottom surface of the functional
transparent plate 17. Accordingly, spaces are formed between the
second upper .lamda./4 retarder 16 and the reflective polarizer 15.
In the case that the functional transparent plate 17 and the second
upper .lamda./4 retarder 16 are produced as separate films, an
assembly process to bond the two films using an adhesive agent is
further required. However, this method does not require such a
process.
[0158] The second method is to attach the second upper .lamda./4
retarder 16 onto the reflective polarizer 15 and then to dispose
the functional transparent plate 17 on the second upper .lamda./4
retarder 16. In this case, spaces are formed between the functional
transparent plate 17 and the second upper .lamda./4 retarder
16.
[0159] In both methods, the spaces may be filled with the air. In
this case, however, a problem may occur that light entering through
an upper layer forming the spaces is totally reflected when
impacting the air that fills the spaces, so the light does not
reach a lower layer forming the spaces. To solve this problem, it
is preferable to fill the spaces with a material with a refractive
index that is very similar to an average of refractive indices of
the upper layer and lower layer. For example, an organic
silicon-based material, such as silicon resin or the like can be
used as the filling material.
[0160] Instead of the functional transparent plates 17 as shown in
FIG. 2 and FIG. 13, other functional transparent plates 17 having
variously forms of modified top or bottom surfaces can be used. In
all cases, it is preferable to form the first facets 17-1 and the
second facets 17-2 at the functional transparent plate 17 to enable
the total reflection to occur there, but it is not necessary that
either surface of the functional transparent plate 17 has a planar
structure or a prismatic structure. To optimize an optical system
of the LCD, the form of the functional transparent plate 17 should
be designed to allow the partial reflection and the total
reflection to occur between the upper surface of the second upper
.lamda./4 retarder 16 and the functional transparent plate 17 in
desired manners. In other word, it is preferable to design the form
of the functional transparent plate 17 in order for the functional
transparent plate 17 to improve utilization efficiency of exterior
light and display characteristics, such as viewing angle, contrast,
and the like.
[0161] In the above-mentioned embodiment, the upper polarizer 22 is
provided under the reflective polarizer 15. Here, the two
polarizers 22 and 15 have the same transmission axes. Accordingly,
even if the upper polarizer 22 is omitted, the results are not
changed. In fact, the reflective polarizer 15 has a relatively low
polarization performance compared with the upper polarizer 22
(which is an absorption-type polarizer). Accordingly, after passing
through the reflective polarizer 15, light still contains a partial
portion of a component that should ordinarily be reflected by the
reflective polarizer. In the case that this phenomenon can be
treated as a minor problem or the thickness of the LCD and the
production cost are treated as the most important matters, the
upper polarizer 22 may be omitted even though contrast of display
images degrades.
[0162] In the above-mentioned embodiment, the TN LC material is
used for the LC layer 3. However, a VA mode or an ECB mode LC
material may also be used instead of the TN LC. Also, the common
electrode 270 and the transparent electrodes 192 or the reflective
electrodes 194 of the pixel electrodes 190 may be formed on the
same insulating substrate using an in-plane switching
technique.
[0163] FIG. 14 is a cross-sectional view showing variations of the
polarization state of light in a reflective LCD according to still
another embodiment of the present invention.
[0164] Differing from the LCD shown in FIG. 6, this LCD does not
include the lower .lamda./4 retarder 13, the lower polarizer 12, or
the backlight unit 500. In addition, this LCD does not require the
transparent electrodes 192 because it is a reflective LCD.
[0165] Hereinafter, an LCD according to still another embodiment of
the present invention will be described in detail with reference to
FIG. 15 through FIG. 17.
[0166] FIG. 15 is a layout view of an LCD according to another
embodiment of the present invention, and FIG. 16 and FIG. 17 are
schematic cross-sectional views cut along XVI-XVI' and XVII-XVII'
of FIG. 15, respectively.
[0167] Referring to FIG. 15 to FIG. 17, the LCD of this embodiment
includes a TFT array panel 100 and a common electrode panel 200
facing each other, and an LC layer 3 that is interposed
therebetween with LC molecules that are aligned perpendicular or
parallel to the surfaces of the two panels 100 and 200.
[0168] LC molecules in the LC layer 3 may be aligned in a
90.degree. twisted nematic (TN) mode, a vertical alignment (VA)
mode, or an electrically controlled birefringence (ECB) mode.
[0169] The TFT array panel 100 is configured as follows.
[0170] A plurality of gate lines 121 and a plurality of storage
electrode lines 131 are formed on an insulating substrate 110 made
of transparent glass or plastic.
[0171] The gate lines 121 for transmitting gate signals extend
substantially in a horizontal direction, while being separated from
each other. Each gate line 121 includes a plurality of gate
electrodes 124 protruding upward and an end portion 125 having a
relatively large dimension to be connected to an external
device.
[0172] The storage electrode lines 131 extend substantially in a
horizontal direction and are substantially parallel to the gate
lines 121. Each storage electrode line 131 includes a plurality of
storage electrodes 133 protruding upward and downward. The storage
electrode lines 131 receive a predetermined voltage, such as a
common voltage that is applied to a common electrode 270 of the
common electrode panel 200.
[0173] The gate lines 121 and the storage electrode lines 131 are
preferably made of an aluminum-(Al) containing metal such as Al and
an Al alloy, a silver-(Ag) containing metal such as Ag and a Ag
alloy, a copper-(Cu) containing metal such as Cu and a Cu alloy, a
molybdenum (Mo)-containing metal such as Mo and a Mo alloy, chrome
(Cr), titanium (Ti), or tantalum (Ta). The gate lines 121 and the
storage electrode lines 131 may be configured as a multi-layered
structure, in which at least two conductive layers (not shown)
having different physical properties are included. In such a
structure, an upper layer of the two is made of a low resistivity
metal, such as an Al-containing metal, a Ag-containing metal, a
Cu-containing metal, or the like, in order to reduce delay of the
signals or voltage drop in the gate lines 121 and the storage
electrode lines 131, and a lower layer is made of material having
prominent physical, chemical, and electrical contact properties
with other materials such as indium tin oxide (ITO), indium zinc
oxide (IZO), etc. For example, a Mo-containing metal, Cr, Ta, Ti,
etc., may be used for the formation of the same layer. A desirable
example of the combination of the two layers is a lower Cr layer
and an upper Al--Nd layer. However, the gate lines 121 and the
storage electrode lines 131 may be configured as single-layered
structures.
[0174] All lateral sides of the gate lines 121 and the storage
electrode lines 131 preferably slope in the range from about
20.degree. to 80.degree. to the surface of the substrate 110.
[0175] A gate insulating layer 140 made of SiN.sub.x or SiO.sub.2
is formed on the gate lines 121 and the storage electrode lines
131.
[0176] A plurality of linear semiconductors 151 made of
hydrogenated amorphous silicon (abbreviated as "a-Si") or
polysilicon are formed on the gate insulating layer 140. Each
linear semiconductor 151 extends substantially in a vertical
direction and includes a plurality of projections 154 that extend
along the respective gate electrodes 124 and a plurality of
extensions 157 that extend from the respective projections 154. The
linear semiconductors 151 are enlarged in the vicinities of the
gate lines 121 and the storage electrode lines 131 to cover them
entirely.
[0177] A plurality of linear ohmic contacts 161 and island-shaped
ohmic contacts 165 are formed on the linear semiconductors 151. The
ohmic contacts 161 and 165 may be made of N+ hydrogenated amorphous
silicon that is highly doped with N-type impurities, or silicide.
The linear ohmic contacts 161 include a plurality of projections
163. A set of a projection 163 and an island-shaped ohmic contact
165 is placed on the projection 154 of the semiconductor 151.
[0178] All lateral sides of the semiconductors 151 and the ohmic
contacts 161 and 165 slope in the range from about 20.degree. to
80.degree. to the surface of the substrate 110.
[0179] A plurality of data lines 171 and a plurality of drain
electrodes 175, separated from the data lines 171, are formed on
the ohmic contacts 161 and 165 and the gate insulating layer
140.
[0180] The data lines 171 for transmitting data signals extend
substantially in a vertical direction to be crossed with the gate
lines 121 and the storage electrode lines 131. Each data line 171
includes an end portion 179 having a relatively large dimension to
be connected to a different layer or an external device.
[0181] Each drain electrode 175 includes an expansion 177 that is
overlapped with one of the storage electrodes 133. Each data line
171 further includes a plurality of source electrodes 173
protruding along and extending toward the respective gate
electrodes 124. Each source electrode 173 surrounds a partial
portion of a bar-shaped end portion of the drain electrode 175.
[0182] A gate electrode 124, a source electrode 173, a drain
electrode 175, and a projection 154 of the semiconductor 151 form a
thin film transistor (TFT). A TFT channel is formed in the
projection 154 provided between the source electrode 173 and the
drain electrode 175.
[0183] The data lines 171 and the drain electrodes 175 are
preferably made of a refractory metal, such as a Mo-containing
metal, a Cr-containing metal, Ta, Ti, or the like, and may be
configured as multi-layered structures including a lower layer (not
shown) consisting of one among Mo, a Mo alloy, Cr, etc., and an
upper layer (not shown) consisting of an Al-containing metal.
[0184] Similarly to the gate lines 121 and the storage electrode
lines 131, all lateral sides of the data lines 171 and the drain
electrodes 175 slope in the range from about 20.degree. to
80.degree. to the surface of the substrate 110.
[0185] The ohmic contacts 161 and 165 exist only between the
underlying semiconductors 151 and the overlying data lines 171 and
between the overlying drain electrodes 175 and the underlying
semiconductors 151, in order to reduce contact resistance
therebetween. The linear semiconductors 151 are partially exposed
at places where the data lines 171 and the drain electrodes 175 do
not cover them, as well as between the source electrodes 173 and
the drain electrodes 175.
[0186] A passivation layer 180, made of an inorganic material such
as SiN.sub.x or SiO.sub.x, is formed on the data lines 171, the
drain electrodes 175, and the exposed portions of the
semiconductors 151.
[0187] An organic insulating layer 187, made of a photosensitive
organic insulator having a prominent planarization property, is
formed on the passivation layer 180. A top surface of the organic
insulating layer 187 is uneven. Due to the uneven surface,
reflective electrodes 194 overlying the organic insulating layer
187 have uneven top surfaces. The uneven top surfaces of the
reflective electrodes 194 prevent mirror reflection. Accordingly,
images that may be shown on an LCD screen due to the mirror
reflection are eliminated. The organic insulating layer 187 is
removed at the end portions 125 and 179 of the gate lines 121 and
the data lines 171, so only the passivation layer 180 remains on
the end portions 125 and 179.
[0188] The passivation layer 180 is provided with a plurality of
contact holes 183, through which the end portions 179 of the data
lines 171 are exposed. A plurality of contact holes 182 are formed
in the passivation layer 180 and the gate insulating layer 140, and
the end portions 125 of the gate lines 121 are exposed
therethrough. A plurality of contact holes 185 are formed in the
passivation layer 180 and the organic insulating layer 187, and the
expansions 177 of the drain electrodes 175 are exposed
therethrough. The contact holes 182, 183, and 185 may have
polygonal or circular shapes. The sidewalls of the contact holes
182, 183, and 185 slope in the range from about 30.degree. to
85.degree. to the surface of the substrate 110 or are shaped as
steps.
[0189] A plurality of pixel electrodes 190 are formed on the
organic insulating layer 187.
[0190] Each pixel electrode 190 includes a transparent electrode
192 and a reflective electrode 194 overlying the transparent
electrode 192. The transparent electrodes 192 are made of a
transparent conductive material such as ITO or IZO, and the
reflective electrodes 194 are made of a reflective opaque material
such as Al, an Al alloy, Ag, or a Ag alloy. Each pixel electrode
190 may further include a contact assistant (not shown) made of Mo,
a Mo alloy, Cr, Ti, or Ta. The contact assistants ensure contact
properties between the transparent electrodes 192 and the
reflective electrodes 194, while preventing the transparent
electrodes 192 from oxidizing the reflective electrodes 194.
[0191] Each pixel is divided into a transmission area TA without
the reflective electrode 194 and a reflection area RA with the
reflective electrode 194. The organic insulating layer 187 is
removed at in the transmission area TA, so that a transmission
window 195 is formed there. Due to the transmission window 195, a
cell gap of the transmission area TA becomes nearly twice as large
as that of the reflection area RA, so that a light path difference
between the transmission area TA and the reflection area RA is
compensated.
[0192] The pixel electrodes 190 are physically and electrically
connected to the expansions 177 of the drain electrodes 175 through
the contact holes 185 to receive data voltages from the drain
electrodes 175. The pixel electrodes 190 supplied with the data
voltages generate electric fields in cooperation with the common
electrode 270 of the common electrode panel 200, determining the
molecular orientation of the LC layer 3 interposed between the two
electrodes.
[0193] Each set of the pixel electrode 190 and the common electrode
270 forms an LC capacitor that is capable of storing the applied
voltage after the TFT is turned off. To enhance the voltage storage
ability of the LC capacitors, storage capacitors, connected to the
LC capacitors in parallel, are further provided. Overlapping of the
expansions 177 of the drain electrodes 175 with the storage
electrodes 133 implements the storage capacitors. Otherwise,
overlapping of the pixel electrodes 190 with the gate lines 121
adjacent thereto may implement the storage capacitors. In this
case, the storage electrode lines 131 may be omitted.
[0194] The pixel electrodes 190 may be overlapped with the data
lines 171 adjacent thereto as well as the gate lines 121 adjacent
thereto, in order to increase the aperture ratio, but such overlap
portions are not always necessary.
[0195] The pixel electrodes 190 may be made of a transparent
conductive polymer. However, opaque reflective metals may be used
in reflective LCDs.
[0196] A plurality of contact assistants 95 and 97 are formed on
the passivation layer 180 relating to a pad portion, and are
individually connected to the end portions 125 of the gate lines
121 and the end portions 179 of the data lines 171 through the
contact holes 182 and 183. The contact assistants 95 and 97
supplement adhesion between the end portions 125 and 179 and
exterior devices, and to protect them. The contact assistants 95
and 97 may be formed on the same layer as the transparent
electrodes 192 or the reflective electrodes 194. However, they may
be omitted because they are not essential elements.
[0197] The common electrode panel 200 facing the TFT array panel
100 is configured as follows.
[0198] A light-blocking member 220 called a "black matrix" is
provided on an insulating substrate 210 made of a transparent
insulating material such as glass. The light-blocking member 220
prevents light from leaking out through barriers between the pixel
electrodes 190 and delimits aperture regions facing the pixel
electrodes 190.
[0199] A plurality of color filters 230 are formed on the substrate
210 and the light-blocking member 220, and most of them are placed
within the aperture regions delimited by the light-blocking member
220. Each color filter 230 is formed between the two adjacent data
lines 171 in a vertical direction, and exhibits one among red,
green, and blue colors. The color filters 230 are connected to one
another in the form of stripes.
[0200] In the case of a typical transflective LCD, in the
transmission areas TA, light passes through the color filters 230
only once, while it passes twice in the reflection areas RA.
Accordingly, a difference of color tone between the transmission
areas TA and the reflection areas RA is generated. To reduce the
difference of color tone between the two areas TA and RA, two
methods can be used. The first method is to form the thickness of
each color filter 230 differently depending on its location. That
is, in this method, a portion of the color filter 230, which is
placed at the transmission area TA, is formed thicker than the
remaining portion, which is placed at the reflection area RA. The
second method is to form light holes in the reflection areas RA of
the color filters 230.
[0201] The common electrode 270, made of a transparent conductive
material such as ITO or IZO, is formed on the light-blocking member
220 and the color filters 230.
[0202] The LC layer 3 is interposed between the two panels 100 and
200 facing each other.
[0203] A lower polarizer 12 and an upper polarizer 22 are
individually attached to the outer surfaces of the two panels 100
and 200. A transmission axis (.theta.) of the upper polarizer 22
and a transmission axis (.theta.+90.degree.) of the lower polarizer
12 are mutually crossed at a right angle.
[0204] A lower .lamda./4 retarder 13 is interposed between the TFT
array panel 100 and the lower polarizer 12, and a first upper
.lamda./4 retarder 14 is interposed between the common electrode
panel 200 and the upper polarizer 22.
[0205] A second upper .lamda./4 retarder 16 is provided on the
upper polarizer 22, and a selective reflection layer 18 is provided
thereon.
[0206] A functional transparent plate 17 is provided on the
selective reflection layer 18. A top surface of the functional
transparent plate 17 consists of a plurality of prisms. Each prism
includes a first facet 17-1, on which no additional material
exists, and a second facet 17-2, on which a cholesteric LC layer
exists.
[0207] Hereinafter, the structure of the above-mentioned LCD and
the polarization principles of light in the same LCD will be
described in detail.
[0208] FIG. 18 shows a vertical scheme of an LCD of another
embodiment of the present invention.
[0209] Referring to FIG. 18, a display panel assembly 300 comprises
a TFT array panel 100 and a common electrode panel 200, and an LC
layer 3 interposed therebetween.
[0210] The lower .lamda./4 retarder 13 is attached to a lower
surface of the display panel assembly 300, and the lower polarizer
12 is attached to a lower surface of the lower .lamda./4 retarder
13.
[0211] Meanwhile, the first upper .lamda./4 retarder 14 is attached
to an upper surface of the display panel assembly 300, and the
upper polarizer 22 is attached to an upper surface of the first
upper .lamda./4 retarder 14. The second upper .lamda./4 retarder 16
and the selective reflection layer 18 in this order are attached to
an upper surface of the upper polarizer 22. The functional
transparent plate 17, of which the top surface consists of the
first sides 17-1 and second sides 17-2, is formed on the selective
reflection layer 18.
[0212] Hereinafter, the above-mentioned structure will be described
in more detail.
[0213] The polarizers 12 and 22 are individually attached to the
outer surfaces of the panels 100 and 200. Their transmission axes
are mutually crossed at a right angle. The polarizers 12 and 22 are
absorption-type polarizers that transmit only linearly polarized
incident light that vibrates parallel to their transmission axes
and absorbs linearly polarized incident light that vibrates
perpendicular to the axes.
[0214] The LCD of this embodiment utilizes three .lamda./4
retarders in all. Each of the three .lamda./4 retarders 13, 14, and
16 converts circularly polarized light into linearly polarized
light or linearly polarized light into circularly polarized light
by causing a phase difference of a quarter wavelength between two
polarized components that are orthogonal to each other and are
individually parallel to a fast axis and a slow axis thereof. The
above-mentioned circularly polarized light may be elliptically
polarized light in actuality, but the elliptically polarized light
will be also referred to as circularly polarized light for
convenience.
[0215] The fast axes of the three .lamda./4 retarders 13, 14, and
16 are preferably formed at .+-.45.degree. to the transmission axes
(.theta.and .theta.+90.degree.) of the polarizers 12 and 22 to
maximize the phase difference between the two polarized components.
However, they may be disposed at different angles, except being
disposed perpendicular to or parallel to each other.
[0216] The selective reflection layer 18 is attached to the upper
surface of the second upper .lamda./4 retarder 16. The selective
reflection layer 18 allows only circularly polarized light in a
specific direction to pass, while reflecting circularly polarized
light in a direction that is opposite to the specific direction. In
this embodiment, the selective reflection layer 18, which
selectively transmits the circularly polarized light, consists of
cholesteric LC material. In detail, the selective reflection layer
18 transmits circularly polarized incident light rotating in the
same direction as an optical axis of the cholesteric LC material,
while reflecting circularly polarized incident light rotating in an
opposite direction. In general, the cholesteric LC material can be
aligned in various alignment manners. However, in this embodiment,
a cholesteric LC material of a planar-alignment mode where spiral
axes of LC molecules are aligned perpendicular to the surfaces of
the substrates is preferably used, in order for the selective
reflection layer 18 to selectively reflect or transmit the
circularly polarized light. A fabrication method of the selective
reflection layer 18 will be described later.
[0217] The functional transparent plate 17 is made of a transparent
material and has a prismatic top surface consisting of a plurality
of first facets 17-1 and a plurality of second facets 17-2, as
shown in FIG. 16. No additional material exists on the first facets
17-1, while the cholesteric LC layer 3 exists on the second facets
17-2. The second facets 17-2 transmit circularly polarized incident
light rotating in the same direction as the optical axis of the
cholesteric LC layer, while reflecting circularly polarized
incident light rotating in an opposite direction. A fabrication
method of the first facets 17-1 and the second facets 17-2 will be
described later.
[0218] The functional transparent plate 17, the selective
reflection layer 18, the second upper .lamda./4 retarder 16, the
upper polarizer 22, the first upper .lamda./4 retarder 14, the
display panel assembly 300, the lower .lamda./4 retarder 13, and
the lower polarizer 12 are bonded by an adhesive agent, in that
order.
[0219] FIG. 19 shows variations of the polarization state of light
at an upper part of the LCD with the functional transparent plate
17, the selective reflection layer 18, the second upper .lamda./4
retarder 16, and the upper polarizer 22.
[0220] As shown in FIG. 19, light that is incident onto the
functional transparent plate 17 is divided into four light rays (A,
B-1, B-2, and C) depending on incident position and incident
angle.
[0221] Incident light (A) of the four is first described.
[0222] The light (A), which is incident onto the second facets 17-2
of the functional transparent plate 17, is separated into two
individual light rays (A-1) and (A-2) having different light paths.
That is, when the light (A) impacts the second facets 17-2 where
the cholesteric LC layer is formed, right-handed circularly
polarized light (A-1) of the incident light (A), which rotates in
the same direction as the optical axis of the cholesteric LC layer,
passes through the functional transparent plate 17, while
left-handed circularly polarized light (A-2), which rotates in an
opposite direction, is reflected.
[0223] The light (A-1) passing through the functional transparent
plate 17 is then incident onto the selective reflection layer 18.
At this time, the selective reflection layer 18 transmits the
right-handed circularly polarized incident light (A-1) since it is
designed to allow right-handed circularly polarized light to pass
and to reflect left-handed circularly polarized light. Next, the
right-handed circularly polarized light (A-1) travels through the
second upper .lamda./4 retarder 16. At this time, the light (A-1)
is converted into linearly polarized light in the X direction by
the second upper .lamda./4 retarder 16. Next, the linearly
polarized light (A-1) passes through the upper polarizer 22 whose
transmission axis is in the X direction.
[0224] Meanwhile, the left-handed circularly polarized reflected
light (A-2), reflected the second facets 17-2, passes through the
first facets 17-1 and is then reflected again by an adjacent second
facet 17-2. The polarization state of the light (A-2) is maintained
with no change during these sequential processes. This is possible
because the second facets 17-2 that are formed with the cholesteric
LC material do not cause any change in the polarization state of
the light when reflecting. Next, the left-handed circularly
polarized light (A-2) is total reflected by the selective
reflection layer 18. The light that is reflected by the selective
reflection layer 18 is designated as (A-3) in FIG. 19.
[0225] Two light rays (B-1) and (B-2) of FIG. 19 are described
below.
[0226] Both of the light rays (B-1) and (B-2) are incident onto the
first facets 17-1 of the functional transparent plate 17, but have
different incident angles. That is, the light (B-1) is slantingly
incident onto the first facets 17-1 of the functional transparent
plate 17, while the light (B-2) is perpendicularly incident onto
the first facets 17-1. Regardless of the different incident angles,
the two light rays (B-1) and (B-2) proceed along the same light
path with the same polarization states after entering the
functional transparent plate 17. In detail, the two light rays
(B-1) and (B-2) pass through the functional transparent plate 17
with all-directional polarized components. Next, the light rays
(B-1) and (B-2) are incident onto the selective reflection layer
18. At this time, the selective reflection layer 18 transmits only
right-handed circularly polarized light rays (B1-1) and (B2-1) of
the incident rays (B-1) and (B-2) and reflects the left-handed
circularly polarized light rays (B1-2) and (B2-2). After this
process, the right-handed circularly polarized light rays (B1-1)
and (B2-1) enters the second upper .lamda./4 retarder 16, thereby
being converted into linearly polarized light rays in the X
direction. Then, the linearly polarized light rays (B1-1) and
(B2-1) travel through the upper polarizer 22.
[0227] Next, light (C) of FIG. 19 is described.
[0228] The light (C) that is perpendicularly incident onto the
second facets 17-2 of the functional transparent plate 17 is also
divided into two separate light rays (C-1) and (C-2) having
different light paths. That is, right-handed circularly polarized
light (C-1) of the incident light (C), which rotates in the same
direction as the optical axis of the cholesteric LC, passes through
the functional transparent plate 17 and then proceeds along the
same light path as the light (A-1), while left-handed circularly
polarized light (C-2) of the incident light (C), which rotates in
the opposite direction, is directed to the outside by reflection at
the second facets 17-2.
[0229] Here, plane angles of the first facets 17-1 and the second
facets 17-2 may be controlled so that the left-handed circularly
polarized reflected light (C-2) is incident onto the first facets
17-1 again and enters the second upper .lamda./4 retarder 16 after
being reflected or refracted by the functional transparent plate
17.
[0230] In the meantime, the left-handed circularly polarized light
rays (A-3), (B1-2), and (B2-2), reflected by the selective
reflection layer 18, enters the functional transparent plate 17
again. In this case, incident light is designated as (D) in FIG.
19. The light (D) is divided into two light rays (D-1) and (D-2)
depending on incident positions of the light (D). That is, the
light (D-2) is incident onto the first facets 17-1 of the
functional transparent plate 17, while the light (D-1) is incident
onto the second facets 17-2. The two light rays (D-1) and (D-2) are
doubly reflected by the first facets 17-1 and the second facets
17-2, respectively. At this time, the light rays (D-1) and (D-2)
undergo 180.degree. phase changes with the reflection at the first
facets 17-1, so that they are all converted into right-handed
polarized light rays (D-1) and (D-2). Next, the right-handed
polarized lights (D-1) and (D-2) enter the selective reflection
layer 18 again. The selective reflection layer 18 transmits all the
right-handed polarized light rays (D-1) and (D-2) without a change
of the polarization state. Subsequently, the two light rays (D-1)
and (D-2) travel though the second upper .lamda./4 retarder 16,
while being converted into linearly polarized light rays in the X
direction. Then, the linearly polarized lights (D-1) and (D-2) pass
through the upper polarizer 22.
[0231] As described above, the light, which is incident from the
ambient environment through the first facets 17-1 and the second
facets 17-2 of the functional transparent plate 17, does not exit
the LCD after being reflected by the selective reflection layer 18
and is returned to the selective reflection layer 18 again by
changing its polarization direction, so that display luminance of
the LCD in a reflection mode is improved. To accomplish this
effect, it is preferable to design the functional transparent plate
17 so that the first facets 17-1 and the second facets 17-2 thereof
represent the largest possible refractive index difference
therebetween, both having largest possible dimensions. It is also
preferable to form angles between the two facets 17-1 and 17-2 to
be as large as possible. In the case that the difference of the
refractive index between the exterior air and the functional
transparent plate 17 is relatively large, no total reflection
occurs when exterior light enters the functional transparent plate
17, but a total reflection occurs in the case when the light
emerges from the functional transparent plate 17 toward the
outside. Accordingly, utilization efficiency of the exterior light
is improved.
[0232] FIG. 20 is a view for comparing the polarization states of
light when the LCD operates in a reflection mode utilizing exterior
light and in a transmission mode utilizing internal light from a
backlight unit 500.
[0233] In this embodiment, the LC layer 3 consists of TN mode LC
molecules. The TN LC molecules have peculiar optical properties.
That is, they are aligned in a vertical direction when an electric
field is applied, thereby causing no change in the polarization
state of light passing through the LC layer 3, but they are aligned
in a horizontal direction when no electric field is applied,
thereby changing the polarization state of light passing through
the LC layer 3.
[0234] Hereinafter, variations of the polarization states of light
when no electric field is applied to the LC layer 3 will be first
described with reference to FIG. 20.
[0235] In FIG. 20, leftmost light (R1) is incident light from the
ambient environment when no electric field is applied to the LC
layer 3 in a reflection mode. The light (R1) passes through the
upper polarizer 22 as linearly polarized light in the X direction.
Then, the linearly polarized light (R1) enters the first upper
.lamda./4 retarder 14. At this time, the first upper .lamda./4
retarder 14 converts the light (R1) into right-handed circularly
polarized light. The right-handed circularly polarized light (R1)
enters the LC layer 3 after passing through the upper insulating
substrate 210 and the color filters 230. In this case, since the LC
layer 3 is supplied with no electric field, the light (R1) is
converted into linearly polarized light in the Y direction. The
linearly polarized light (R1) rotates by 180.degree. with the
reflection at the reflective electrode 194. However, the light (R1)
maintains the polarization state without a change even after the
rotation. The reflected light (R1) is converted into right-handed
circularly polarized light again when passing through the LC layer
3, and then enters the first upper .lamda./4 retarder 14 after
successively passing through the color filters 230 and the upper
insulating substrate 210. At this time, the first upper .lamda./4
retarder 14 converts the right-handed circularly polarized light
(R1) into linearly polarized light in the X direction. Next, the
linearly polarized light (R1) enters the second upper .lamda./4
retarder 16 after passing through the upper polarizer 22. At this
time, the linearly polarized light in the X direction (R1) is
converted into right-handed circularly polarized light by the
second upper .lamda./4 retarder 16. Subsequently, the right-handed
circularly polarized light (R1) passes through the selective
reflection layer 18 and the functional transparent plate 17 without
a change of the polarization state, and then exits the LCD. At this
time, the LCD screen is shown as a white state.
[0236] Meanwhile, light (T1) of FIG. 20 is light supplied from an
internal light source of the LCD, i.e., the backlight unit 500,
when no electric field is applied to the LC layer 3 in a
transmission mode. First, the light (T) passes through the lower
polarizer 13. In this step, only a linearly polarized component in
the Y direction of the light (T) is transmitted and the remaining
components are removed by absorption. The linearly polarized
component in the Y direction (T) is converted into left-handed
circularly polarized light (Ti) by the lower .lamda./4 retarder 13.
The left-handed circularly polarized light (T1) enters the LC layer
3 after passing through the lower insulating substrate 110, and is
then converted into right-handed circularly polarized light when
passing through the LC layer 3. Next, the right-handed circularly
polarized light (T1) passes through the color filters 230 and the
upper insulating substrate 210 and then enters the first upper
.lamda./4 retarder 14. At this time, the light (T1) is converted
into linearly polarized light in the X direction by the first upper
.lamda./4 retarder 14. Next, the linearly polarized light (T1)
passes through the upper polarizer 22 and then enters the second
upper .lamda./4 retarder 16, thereby being converted into
right-handed circularly polarized light by the second upper
.lamda./4 retarder 16. Subsequently, the right-handed circularly
polarized light (T1) passes through the selective reflection layer
18 and the functional transparent plate 17 without a change of the
polarization state, and then exits the LCD. At this time, the LCD
screen is shown as a white state.
[0237] Hereinafter, variations of the polarization states in the
case of the field-applied LC layer 3 will be described with
reference to FIG. 20.
[0238] In FIG. 20, light (R2) is incident light from the ambient
environment when an electric field is applied to the LC layer 3 in
a reflection mode. The light (R2) passes through the upper
polarizer 22 as linearly polarized light in the X direction. Next,
the linearly polarized light in the X direction (R2) enters the
first upper .lamda./4 retarder 14. At this time, the first upper
.lamda./4 retarder 14 converts the light (R2) into right-handed
circularly polarized light. The right-handed circularly polarized
light (R2) enters the LC layer 3 after passing through the upper
insulating substrate 210 and the color filters 230. In this case,
the field-applied LC layer 3 does not cause a change in the
polarization state of the light passing therethrough. Sequentially,
the right-handed circularly polarized light (R2) rotates by
180.degree. with the reflection at the reflective electrodes 194,
thereby being converted into left-handed circularly polarized
light. The left-handed circularly polarized light (R2), reflected
by the reflective electrodes 194, passes through the LC layer 3
again without a change of the polarization state, and then enters
the first upper .lamda./4 retarder 14 after passing through the
color filters 230 and the upper insulating substrate 210. At this
time, the first upper .lamda./4 retarder 14 converts the
left-handed circularly polarized light (R2) into linearly polarized
light in the Y direction. Next, the upper polarizer 22 absorbs all
of the linearly polarized light in the Y direction (R2), so that no
light exits the LCD. In this case, the LCD screen is shown as a
black state.
[0239] Meanwhile, light (T2) of FIG. 20 is light supplied from an
internal light source, i.e., a backlight unit 500, when an electric
field is applied to the LC layer 3 in a transmission mode. The
light (T) supplied from the backlight unit 500 passes through the
lower polarizer 13. In this step, only a linearly polarized
component in the Y direction of the light (T) remains and the
remaining components are removed. The linearly polarized component
in the Y direction (T) is converted into left-handed circularly
polarized light (T2) by the lower .lamda./4 retarder 13. The
left-handed circularly polarized light (T2) enters the LC layer 3
after passing through the lower insulating substrate 110, and then
exits the LC layer 3 with no change of the polarization state.
Next, the left-handed circularly polarized light (T2) passes
through the color filters 230 and the upper insulating substrate
210, and then enters the first upper .lamda./4 retarder 14. At this
time, the light (T2) is converted into linearly polarized light in
the Y direction by the first upper .lamda./4 retarder 14. Next, the
upper polarizer 22 completely absorbs the linearly polarized light
in the Y direction (T2), so that no light exits the LCD. At this
time, the LCD screen is shown as a black state.
[0240] As described above, regardless of the operation modes of the
LCD, the LCD screen exhibits the black state when the field is
applied to the LC layer 3, while it exhibits the white state when
the field is not applied to the LC layer 3.
[0241] FIG. 21 through FIG. 24 are schematic cross-sectional views
showing process steps to manufacture a selective reflection layer
18 of an LCD according to another embodiment of the present
invention.
[0242] The selective reflection layer 18 is manufactured as
follows.
[0243] An optical alignment agent is first coated on a second upper
.lamda./4 retarder 16, and is then exposed to light, thereby
forming an optical alignment layer 25 as shown in FIG. 21. Next, as
shown in FIG. 22, a cholesteric LC material 45 containing a UV
cross-linking agent is coated over the optical alignment layer 25.
At this time, it is preferable that molecules in the LC layer 3
have planar orientations. Subsequently, UV irradiation is applied
to the resultant structure of FIG. 22, as shown in FIG. 23, to cure
the cholesteric LC material 45. As a result, a cholesteric LC layer
46 is formed. The cholesteric LC layer 46 and the optical alignment
layer 25 form a selective reflection layer 18, as shown in FIG.
24.
[0244] In the above, the selective reflection layer 18 is formed on
the second upper .lamda./4 retarder 16, but it may be formed on a
different substrate and separately prepared.
[0245] FIG. 25 through FIG. 30 are schematic cross-sectional views
showing process steps to manufacture a functional transparent plate
17 of an LCD according to another embodiment of the present
invention.
[0246] The functional transparent plate 17 is manufactured as
follows.
[0247] As shown in FIG. 25, after the functional transparent plate
17 with a prismatic top surface, which consists of first facets
17-1 and second facets 17-2, is first formed, an optical alignment
agent 20 is coated thereon. The resultant structure of FIG. 25 then
is selectively exposed to light through a first mask 30 as shown in
FIG. 26. After exposure, a development process is performed. As a
result, an optical alignment layer 21 is formed only on the second
facets 17-2, as shown in FIG. 27. Subsequent to the formation of
the optical alignment layer 21, a cholesteric LC material 40 is
coated on the functional transparent plate 17, as shown in FIG. 28.
Next, the resultant structure of FIG. 28 is selectively exposed to
light through a second mask 35, as shown in FIG. 29. Then, as shown
in FIG. 30, development and UV curing processes are successively
performed, so that a cholesteric LC layer 41 is formed only on the
second facets 17-2. As a result, each second facet 17-2 consists of
the optical alignment layer 21 and the cholesteric LC layer 41.
[0248] FIG. 31 is a schematic cross-sectional view of a functional
transparent plate of an LCD according to still another embodiment
of the present invention.
[0249] Referring to FIG. 31, the functional transparent plate 17 of
this embodiment has a top surface with first facets 17-1 and second
facets 17-2 that are inwardly formed from the surface thereof, and
a prismatic bottom surface that is similar to the top surface of
the functional transparent plate 17 of the previous embodiment. In
this structure, it is preferable that first apexes P1 and second
apexes P3 of the bottom surface and third apexes P2 of the top
surface are positioned on different vertical lines from each other.
This is because such a structure enables much of the reflected
light to reach the cholesteric LC layer 41 of the second facets
17-2, thus improving utilization efficiency of the light.
[0250] In this structure, an important problem is how to attach the
functional transparent plate 17 with the prismatic bottom surface
onto the selective reflection layer 18. Two possible methods are
discussed below.
[0251] The first method is to directly form the selective
reflection layer 18 on the bottom surface of the functional
transparent plate 17. In this case, the selective reflection layer
18 has the same form as the bottom surface of the functional
transparent plate 17. Accordingly, spaces are formed between the
selective reflection layer 18 and the second upper .lamda./4
retarder 16. In the case that the functional transparent plate 17
and the selective reflection layer 18 are produced as separated
films, an assembly process to bond the two films using an adhesive
agent is additionally required. However, this method does not
require such a process.
[0252] The second method is to attach the selective reflection
layer 18 onto the second upper .lamda./4 retarder 16 and then to
dispose the functional transparent plate 17 thereon. In this case,
spaces are formed between the selective reflection layer 18 and the
functional transparent plate 17.
[0253] In both methods, the spaces may be filled with the air. In
this case, however, a problem may occur in which light entering
through an upper layer forming the spaces is totally reflected when
impacting the air that fills the spaces, so the light does not
reach a lower layer forming the spaces. To settle this problem, it
is preferable to fill the spaces with a material with a refractive
index that is very similar to an average of refractive indices of
the upper layer and lower layer. For example, an organic
silicon-based material, such as silicon resin or the like, can be
used as the filling material.
[0254] Instead of the functional transparent plates 17 as shown in
FIG. 16 and FIG. 31, other functional transparent plates 17 having
variously forms of modified top or bottom surfaces can be used. In
all cases, it is preferable to form the first facets 17-1 and the
second facets 17-2 at the functional transparent plate 17 to enable
the total reflection to occur at there, but it is not necessary
that either surface of the functional transparent plate 17 has a
planar structure or a prismatic structure. To optimize an optical
system of the LCD, the form of the functional transparent plate 17
should be designed to allow the partial reflection and the total
reflection to occur between the upper surface of the second upper
.lamda./4 retarder 16 and the functional transparent plate 17 in
desired manners. In other words, it is preferable to design the
form of the functional transparent plate 17 in order for the
functional transparent plate 17 to improve utilization efficiency
of exterior light and display characteristics, such as viewing
angle, contrast, and the like.
[0255] In the above-mentioned embodiment, the TN LC material is
used for the LC layer 3. However, a VA mode or an ECB mode LC
material may also be used instead of the TN LC. Also, the common
electrode 270 and the transparent electrodes 192 or the reflective
electrodes 194 of the pixel electrodes 190 may be formed on the
same insulating substrate using an in-plane switching
technique.
[0256] FIG. 32 is a cross-sectional view showing variations of the
polarization state of light in a reflective LCD according to still
another embodiment of the present invention.
[0257] Differing from the transflective LCD of FIG. 20, this LCD
does not include the lower .lamda./4 retarder 13, the lower
polarizer 12, or the backlight unit 500. In addition, this LCD does
not require the transparent electrodes 192 because it is a
reflective LCD.
[0258] As described above, in the reflective or Tran missive LCD
according to an aspect of the present invention, the reflective
polarizer, the .lamda./4 retarder, and the functional transparent
plate with the first facets and the second facets, which are
disposed on the display panel assembly in that order, improve
utilization efficiency of light incident from the ambient
environment so that display luminance of the LCD operating in a
reflection mode is improved.
[0259] Alternately, in the reflective or transmissive LCD according
to another aspect of the present invention, the .lamda./4 retarder,
the selective reflection layer, and the functional transparent
plate with the first facets and the second facets, which are
disposed on the display panel assembly in that order, improve
utilization efficiency of light incident from ambient environment
so that display luminance of the LCD operating a reflection mode is
improved.
[0260] The present invention should not be considered limited to
the particular examples described above, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention may be applicable will be readily apparent to those of
skill in the art to which the present invention is directed upon
review of the instant specification.
* * * * *